the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

silica diagenesis ii general mechanisms abstract amorphous silica phases opal a precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions opal a dissolves and yields solutions of still relatively high silica content in pore waters containing abundant cations open framework polymers form which flocculate to yield opal ct opal ct becomes increasingly ordered primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase opal ct dissolves to yield pore waters of low silica concentration which allows slow growth of quartz crystals from monomeric solution the quartz crystals then slowly increase in size and crystallinity carbonates appear to enhance opal ct formation possibly due to the activity of positively charged hydroxyl complexes hence polymerization in relatively pure systems is involved in opal a formation and polymerization in impure systems is involved in opal ct formation and slow growth from monomeric low silica concentration solutions is involved in precipitation of quartz in sedimentary realms

hydration state of calcium sulfates in gale crater mars identification of bassanite veins abstract in situ analyses reveal the presence of hydrogen within calcium sulfate veins crosscutting the sediments found in gale crater laboratory experiments were performed to calibrate the hydrogen signal measured by laser induced breakdown spectroscopy libs in a range applicable to martian data the analyses indicate that all veins targeted so far at gale consist predominantly of bassanite which most likely formed by dehydration of gypsum this scenario suggests that the percolating water produced gypsum possibly by hydration of anhydrite in aqueous solution and remained at temperatures below 60 c at that time desiccating conditions followed consistent with a hyperarid climate and favored by burial or impacts additionally anhydrite with lesser bassanite has been found by xrd in samples of sediments hosting the veins our result suggests bassanite is likely found in the veins and anhydrite may be more common as a fine grained component within the sediments

origin of quartz cements in some sandstones from the jurassic of the inner moray firth uk the extent of quartz cementation in shallow marine sandstones of the brora arenaceous formation oxfordian is closely related to the occurrence and abundance of rhaxella perforata sponge spicules three cement morphologies are identified chalcedonic quartz microquartz and mesoquartz chalcedonic quartz forms matrix supported cements which preserve moulds of rhaxella spicules chalcedonic quartz crystals have inequant development of crystal faces on average 0 1 m in diameter and are the first formed cement and reveal homogeneous dark grey tones on the sem cl bei microquartz forms 5 10 m diameter crystals which commonly grow on chalcedonic quartz substrates and show various grey tones under sem cl bei mesoquartz crystals grow in optical continuity with their host grains have 20 m a axial diameter crystals and exhibit distinctly zoned luminescence although no opaline silica is preserved the quartz cement is interpreted to have formed from an opaline precursor detrital quartz has an average 18o composition of 12 2 and mesoquartz syntaxial overgrowth has an average 18o composition of 20 0 estimates of the 18o compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types mixtures of the two give consistently higher 18o compositions than mesoquartz the higher estimate being 39 2 from oxygen isotope data the formation of quartz microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71 c in marine derived pore waters organic and inorganic maturation data constrain the upper temperature limit to less than 60 c

geothermal surface alteration of basalts krýsuvik iceland alteration mineralogy water chemistry and the effects of acid supply on the alteration process abstract the geothermal surface alteration of basalts and associated water chemistry at kr suvik sw iceland were studied the geothermal area was characterised with zones of intensive surface alteration steam vents mud pots and hot springs the steam heated geothermal surface waters had ph values between 1 69 and 7 67 and total dissolved solid tds concentrations between 154 and 6660 ppm with cl and so 4 concentration decreasing and increasing with decreasing ph respectively alteration mineral assemblages observed were strongly associated with the surface intensity in areas of most intensive activity the basaltic rocks were altered to amorphous silica anatase and pyrite with a crust of native sulphur at the surface with decreased activity kaolinite became important as well as iron oxyhydroxides and oxides on the flanks of the area montmorillonite was the predominant alteration product based on these observations the surface geothermal activity was divided into three groups 1 high activity areas with active steam vents and mud pots and intensive acid leaching 2 medium activity areas where the ground is hot steam vents and mud pots are uncommon and the surface alteration is less intensive and 3 low activity areas on the margins of the surface geothermal activity the primary factors influencing the steam heated acid sulphate alteration of basalts included the redox state oxidation front supply of acids and ph and the extent of reaction the formation of iron and sulphur containing minerals and the respective elemental mobility depended on the redox conditions with pyrite formation under reduced conditions and goethite and or hematite under oxidised conditions at low ph ca mg k and na were mobile and leached out whereas fe ti and al and to a large degree si were retained in the alteration product at higher ph values 5 the mobility of ca mg k and na was reduced due to the formation of clays

primary silica precipitate at the precambrian cambrian boundary in the south oman salt basin sultanate of oman abstract an organic rich laminated chert silicilyte consisting of up to 90 microcrystalline quartz that formed at the precambrian cambrian boundary acts as a light oil reservoir in the subsurface of the south oman salt basin sultanate of oman fully encased in salt domes it was first discovered during the 1990 s hydrocarbon exploration activities of petroleum development oman because of the economic significance and the unconventional reservoir characteristics there is great interest in understanding the origin of the laminated chert its source of silica and mode of precipitation in an anoxic sulphur rich stagnant and highly saline basin the homogeneous distribution and high values of stable si isotope composition avg 30 si 0 83 0 28 coupled with a low molar ge si ratio 6 of the microcrystalline matrix quartz clearly reveal dissolved silica in the seawater as the si source whereas hydrothermal or biogenic e g sponge derived silica can be excluded silica precipitation from seawater was likely the result of a dramatic increase in salinity in response to salt dissolution atop and adjacent to the edges of transtensional depressions on the deep basin floor thus markedly reducing the solubility of amorphous silica in these brine filled seawater depressions this saturation triggered the formation of silica gel which accumulated at the basin floor forming a soft silica rich layer on bacterial mats giving rise to a laminated sediment the mean number of laminae is ca 32 per year suggesting that layering is non annual and controlled by processes such as fluctuations in nutrient supply lunar driven re mixing or diagenetic segregation the transformation of the silica gel to microcrystalline quartz occurred below 45 c indicating a less than 4 5 18 o composition of the pore water during microcrystalline quartz formation

chemcam passive reflectance spectroscopy of surface materials at the curiosity landing site mars the spectrometers on the mars science laboratory msl chemcam instrument were used in passive mode to record visible near infrared 400 840 nm radiance from the martian surface using the onboard chemcam calibration targets housing as a reflectance standard we developed methods to collect calibrate and reduce radiance observations to relative reflectance such measurements accurately reproduce the known reflectance spectra of other calibration targets on the rover and represent the highest spatial resolution 0 65 mrad and spectral sampling 1 nm visible near infrared reflectance spectra from a landed platform on mars relative reflectance spectra of surface rocks and soils match those from orbital observations and multispectral data from the msl mastcam camera preliminary analyses of the band depths spectral slopes and reflectance ratios of the more than 2000 spectra taken during the first year of msl operations demonstrate at least six spectral classes of materials distinguished by variations in ferrous and ferric components initial comparisons of chemcam spectra to laboratory spectra of minerals and mars analog materials demonstrate similarities with palagonitic soils and indications of orthopyroxene in some dark rocks magnesium rich raised ridges tend to exhibit distinct near infrared slopes the ferric absorption downturn typically found for martian materials at 600 nm is greatly subdued in brushed rocks and drill tailings consistent with their more ferrous nature calcium sulfate veins exhibit the highest relative reflectances observed but are still relatively red owing to the effects of residual dust such dust is overall less prominent on rocks sampled within the blast zone immediately surrounding the landing site these samples were likely affected by the landing thrusters which partially removed the ubiquitous dust coatings increased dust coatings on the calibration targets during the first year of the mission were documented by the chemcam passive measurements as well ongoing efforts to model and correct for this dust component should improve calibration of the relative reflectance spectra this will be useful as additional measurements are acquired during the rover s future examinations of hematite sulfate and phyllosilicate bearing materials near the base of mt sharp that are spectrally active in the 400 840 nm region

an iron shuttle for deepwater silica in late archean and early paleoproterozoic iron formation iron formations are typically thinly bedded or laminated sedimentary rocks containing 15 or more of iron and a large proportion of silica commonly 40 in the ca 2590 2460 ma campbellrand kuruman complex transvaal supergroup south africa iron formation occurs as a sediment starved deepwater facies distal to carbonates and shales iron minerals primarily siderite define the lamination the silica primarily occurs as thin beds and nodules of diagenetic chert now microcrystalline quartz filling pore space and replacing iron formation minerals and co occurring deepwater lithologies mechanisms proposed to explain precipitation of the iron component of iron formation include photosynthetic oxygen production anoxygenic photosynthesis abiotic photochemistry and chemoautotrophy using fe ii as an electron donor the origin and mechanism of silica precipitation in these deposits have received less attention here we present a conceptual model of iron formation that offers insight into the deposition of silica the model hinges on the proclivity of dissolved silica to adsorb onto the hydrous surfaces of ferric oxides soluble ferrous iron is oxidized in the surface ocean to form ferric hydroxides which precipitate fe oh 3 binds silica and sinks from the surface ocean along with organic matter shuttling silica to basinal waters and sediments fe iii respiration in the sediments returns the majority of iron to the water column but also generates considerable alkalinity in pore waters driving precipitation of siderite from fe2 and respiration influenced co2 silica liberated during iron reduction becomes concentrated in pore fluids and is ultimately precipitated as diagenetic mineral phases this model explains many of the mineralogical textural and environmental features of late archean and earliest paleo proterozoic iron formation

origin of volcanism on the flanks of the pacific antarctic ridge between 41 30 s and 52 s 1 non hot spot intraplate volcanism is a common feature near the east pacific rise or pacific antarctic ridge volcanic ridges and seamount chains tens to hundreds of kilometers long are asymmetrically distributed about the ridge axis with most volcanic features occurring on the pacific plate their origins remain controversial we have analyzed off axis volcanic ridges near the pacific antarctic ridge from bathymetry backscatter gravity and geochemistry data of the pacantarctic 2 cruise k ar dating of samples dredged on these structures reveals a contrast of up to 3 ma between the volcanoes and the underlying crust the volcanic activity as suggested by the strong backscatter in sonar images appears to be limited to areas of seafloor younger than about 3 ma all surveyed ridges north of the menard transform fault tf show recent activity close to the ridge axis and are not affected by faults the off axis volcanic ridges south of the menard tf show recent volcanic flows in their center and are affected by n s extension two different types of volcanoes can be characterized conical flat topped ones and rough elongated ones associated with narrow e w trending volcanic ridges some of them showing strong backscattering on the em12 imagery from the morphology of the seamount chains and the ages of the lava samples we infer that the magma source for the volcanic ridges is related to the feeding of the ridge axis through three dimensional mantle convective circulation we suggest that a change in the relative plate motion since about 5 ma might have induced an offset of the mantle upwelling circulation under the ridge axis so that anomalously hot mantle rises under the pacific ridge flank the kinematic change is also likely responsible for the tectonic deformation in the young lithosphere south of menard tf

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

physical pathways for carbon transfers between the surface mixed layer and the ocean interior 1 although they are key components of the surface ocean carbon budget physical processes inducing carbon fluxes across the mixed layer base i e subduction and obduction have received much less attention than biological processes using a global model analysis of the preindustrial ocean physical carbon fluxes are quantified and compared to the other carbon fluxes in and out of the surface mixed layer i e air sea co2gas exchange and sedimentation of biogenic material model based carbon obduction and subduction are evaluated against independent data based estimates to the extent that was possible we find that climatological physical fluxes of dissolved inorganic carbon dic are two orders of magnitude larger than the other carbon fluxes and vary over the globe at smaller spatial scale at temperate latitudes the subduction of dic and to a much lesser extent 10 the sinking of particles maintain co2undersaturation whereas dic is obducted back to the surface in the tropical band 75 and southern ocean 25 at the global scale these two large counter balancing fluxes of dic amount to 275 5 pgc yr 1 for the supply by obduction and 264 5 pgc yr 1 for the removal by subduction which is 3 to 5 times larger than previous estimates moreover we find that subduction of organic carbon dissolved and particulate represents 20 of the total export of organic carbon at the global scale we evaluate that of the 11 pgc yr 1 of organic material lost from the surface every year 2 1 pgc yr 1 is lost through subduction of organic carbon our results emphasize the strong sensitivity of the oceanic carbon cycle to changes in mixed layer depth ocean currents and wind

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

diagenetic silica enrichment and late stage groundwater activity in gale crater mars diagenetic silica enrichment in fracture associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of aeolis mons in gale crater mars the diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger unconformably draping aeolian sandstone implying that diagenetic silica enrichment postdates the detrital silica enrichment a causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock although absolute timing is uncertain the observed diagenesis likely represents some of the most recent groundwater activity in gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of aeolis mons were deposited

experimental epithermal alteration of synthetic los angeles meteorite implications for the origin of martian soils and identification of hydrothermal sites on mars 1 the dissolution behavior and secondary minerals generated by experimental alteration of a synthetic los angeles basaltic shergottite la were evaluated at epithermal 75 c conditions starting ph values of 1 1 and 3 6 and water rock ratios ranging from 100 to 2000 were studied using flow through and batch reactor experimental apparatus dissolution of plagioclase dominates effluent solution chemistry under all experimental conditions little mg is released to solution because nearly 100 of the mg in unaltered la is contained in pyroxene m1 sites which are relatively resistant to dissolution secondary minerals generated include siliceous residue amorphous sio2 lepidocrocite and ferrihydrite anhydrite alunogen rhomboclase ferrinatrite halite and unidentified ca and na sulfates the dominance of alteration products of plagioclase suggests that la type basalts have not contributed significantly to the martian soils the search for hydrothermal sites by remote sensing may be hampered by the general similarity of the alteration products found in the near surface epithermal environment to those thought to exist in martian soils sulfates iron oxyhydroxides amorphous silica however the unique chemical composition of secondary products formed by la alteration may make detection of recent hydrothermal alteration of evolved basaltic rocks more straightforward in addition alteration in terrestrial epithermal environments associated with mafic to intermediate volcanic rocks generally produces abundant sulfides and kaolinite two potentially unique mineral phases which might also indicate the presence of active or extinct hydrothermal systems

in situ and experimental evidence for acidic weathering of rocks and soils on mars experimental data for alteration of synthetic martian basalts at ph 0 1 indicate that chemical fractionations at low ph are vastly different from those observed during terrestrial weathering rock surface analyses from gusev crater are well described by the relationships apparent from low ph experimental alteration data a model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at gusev this zone is not chemically fractionated to a large degree from the underlying rock interior indicating that the rock surface alteration process has occurred at low water to rock ratio the geochemistry of natural rock surfaces analyzed by apxs is consistent with a mixture between adhering soil dust and the leached alteration zone the chemistry of rock surfaces analyzed after brushing with the rat is largely representative of the leached alteration zone the chemistry of rock surfaces analyzed after grinding with the rat is largely representative of the interior of the rock relatively unaffected by the alteration process occurring at the rock surface elemental measurements from the spirit opportunity pathfinder and viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low ph low water to rock ratio alteration relationships developed for gusev rocks soils are affected principally by mobility of fe and mg consistent with alteration of olivine bearing basalt and subsequent precipitation of fe and mg bearing secondary minerals as the primary control on soil geochemistry copyright 2006 by the american geophysical union

formation of silica by low temperature acid alteration of martian rocks physical chemical constraints 1 theoretical geochemical modeling has been used to evaluate the formation conditions of amorphous silica during aqueous alteration of typical martian igneous rocks at 0 c the models show that some silica can form during low temperature alteration of mafic to ultramafic rocks over a large range of ph and water rock ratios silica dominated deposits like those found at the columbia hills in gusev crater on mars could form at solution ph below 2 and water rock ratios of 102 104 high water rock conditions could represent acid flow through rocks solution discharge from an acid spring and or surface flow of released solutions low ph favors dissolution of silicates and saturation of solution with respect to relatively insoluble silica which then precipitates partial evaporation or freezing of released solutions would also cause precipitation of amorphous silica modeling shows that ti oxides are also present in silica rich deposits more soluble minerals e g ferric oxides phyllosilicates could precipitate downstream from partially neutralized evaporated or frozen solutions temperatures above 0 c are not required to form abundant silica through acid alteration of martian rocks

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

silicic volcanism on mars evidenced by tridymite in high sio2 sedimentary rock at gale crater tridymite a low pressure high temperature 870 c sio2 polymorph was detected in a drill sample of laminated mudstone buckskin at marias pass in gale crater mars by the chemistry and mineralogy x ray diffraction instrument onboard the mars science laboratory rover curiosity the tridymitic mudstone has 40 wt crystalline and 60 wt x ray amorphous material and a bulk composition with 74 wt sio2 alpha particle x ray spectrometer analysis plagioclase 17 wt of bulk sample tridymite 14 wt sanidine 3 wt cation deficient magnetite 3 wt cristobalite 2 wt and anhydrite 1 wt are the mudstone crystalline minerals amorphous material is silica rich 39 wt opal a and or high sio2 glass and opal ct volatile bearing 16 wt mixed cation sulfates phosphates and chlorides perchlorates chlorates and has minor tio2 and fe2o3t oxides 5 wt rietveld refinement yielded a monoclinic structural model for a well crystalline tridymite consistent with high formation temperatures terrestrial tridymite is commonly associated with silicic volcanism and detritus from such volcanism in a lake gale catchment environment can account for buckskin s tridymite cristobalite feldspar and any residual high sio2 glass these cogenetic detrital phases are possibly sourced from the gale crater wall rim central peak opaline silica could form during diagenesis from high sio2 glass as amorphous precipitated silica or as a residue of acidic leaching in the sediment source region or at marias pass the amorphous mixed cation salts and oxides and possibly the crystalline magnetite otherwise detrital are primary precipitates and or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions temperatures and acidities anhydrite is post lithification fracture vein fill

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

pleistocene cold climate groundwater silicification jbel ghassoul region missour basin morocco surficial silicifications have been long considered to be indicative of warm and dry climates here we describe various forms of supergene silicification in a miocene lacustrine sequence in the missour basin near jbel ghassoul morocco in a landscape with accentuated relief the silicification is almost exclusively limited to a 10 40 m wide zone from the edges of scarp and mesa landforms this distribution is interpreted to record the locations where groundwaters which produced the silicification discharged from a higher level palaeolandscape the main component of the silica was imported late and significantly post dates the deposition of the sediments this implies that significant volumes of silica bearing solutions flowed through these formations in response to a hydraulic gradient generated by relief silicification thus occurred only after uplift and incision of the sedimentary fill of the missour basin the zones of silicification of the jbel ghassoul sequence can be linked geomorphologically to remnants of high level pediments that have been dated in the literature to the early to middle pleistocene and interpreted to have been formed during cold climates low temperatures in outcrops near the discharge zones during cold periods are considered to be a key factor in silica precipitation from groundwaters

dissolution of primary minerals in natural waters abstract the saturation state of olivine plagioclase clinopyroxene orthopyroxene fe ti oxides and apatite of variable composition has been assessed in natural waters in iceland with temperature ranging from 0 c to 300 c and in situ ph from below 5 to above 10 cold waters are undersaturated with respect to olivine orthopyroxene clinopyroxene and plagioclases indicating that all these minerals tend to dissolve under weathering conditions with increasing ph and temperature the waters approach saturation with pyroxene olivine and plagioclases also the degree of undersaturation of olivine and orthopyroxene decreases with increasing fe content of the minerals and fe rich olivine and orthopyroxene are stable between 50 c and 150 c whereas mg rich ones tend to dissolve natural waters in iceland are saturated with respect to pure albite when above 50 c they are on the other hand undersaturated with ca rich plagioclase up to 250 c where the waters reach saturation pure magnetite and hematite are stable at all temperatures with increasing titanium content the minerals become unstable and the waters are undersaturated with respect to pure ulvospinel at temperatures up to 300 c pure ilmenite is however close to saturation under weathering conditions but undersaturated above 200 c f apatite is close to saturation at all temperatures on the other hand undersaturation with respect to oh apatite is observed at all temperatures the weathering susceptibilities of primary minerals of basalt in icelandic waters in increasing order are mg olivine fe olivine ti rich magnetite ca plagioclase mg orthopyroxene fe orthopyroxene clinopyroxene na plagioclase f apatite ti rich ilmenite ti poor magnetite ti poor hematite