# Minerals/Blues

Often a mineral appears blue due to the presence of copper or sulfur. Glaucophane is a blue silicate that owes its color to its characteristic formation.

## Colors

Each form of radiation that an astronomical entity can emit, absorb, fluoresce, transmit, or reflect has a spectrum in time, space, intensity, or variation.
A spectrum of variation shows its colors.

## Alloy minerals

"Grain size varies from 98 to 530 lm with an average of *150 lm. Minor [elements] oxidation [from an iron–nickel–chromium–cobalt–phosphorus alloy] is evidenced by the presence of a light brown and blue surface layer composed of very fine-grained (<1 lm) crystals on the surface." "[T]he oxidation of minor elements in metallic alloys in the early solar system" is indicated to possess at instances a blue surface layer.

## Oxidanes

Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of a glacier. Blue ice was observed in Tasman Glacier, New Zealand in January 2011. Ice is blue for the same reason water is blue: it is a result of an overtone of an oxygen-hydrogen (O-H) bond stretch in water which absorbs light at the red end of the visible spectrum.

## Covellites

Covellite [CuS] has been found in veins at depths of 1,150 meters, as the primary mineral. Covellite formed as clusters in these veins reaching one meter across. Covellite is a hexagonal form of CuS. Covellite is a chalcogen.

## Fluorites

Many samples of fluorite exhibit fluorescence under ultraviolet light, a property that takes its name from fluorite. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green and white also occur. The fluorescence of fluorite may be due to mineral impurities such as yttrium, ytterbium, or organic matter in the crystal lattice. In particular, the blue fluorescence seen in fluorites from certain parts of Great Britain responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent europium in the crystal.

## Calcites

Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4.
On the right is blue calcite produced by natural irradiation.

## Hauynes

Hauyne, haüyne or hauynite occurs in Vesuvian lavas in Monte Somma, Italy. It is a tectosilicate mineral with sulfate, with endmember formula Na$_3$Ca(Si$_3$Al$_3$)O$_{12}$(SO$_4$). It is a feldspathoid and a member of the sodalite group. Haüyne occurs in phonolites and related leucite- or nepheline-rich, silica-poor, igneous rocks; less commonly in nepheline-free extrusives and metamorphic rocks (marble).
Haüyne, or haüynite, is cubic, a member of the sodalite group, and has the formula (Na,Ca)$_{4-8}$Al$_6$Si$_6$O$_{24}$(SO$_4$)$_{1-2}$.

## Sodalites

"Sodalite is a rich royal blue mineral ... massive sodalite samples are opaque, crystals are usually transparent to translucent. ... Occurring typically in massive form, sodalite is found as vein fillings in plutonic igneous rocks such as nepheline syenites."
"The following features and examples imply why stress of tectosilicate lattices can be linked to the luminescence emission at 340 nm: (i) natural metastable hatch-cross texture in exsolved Na/K microcline at 300 K, (ii) radiation damaged areas in natural quartz, (iii) natural quartz with large amounts of silicon substitution with aluminum and alkali ions, (iv) artificial porous silica with OH groups adsorbed to the surfaces, (v) sodalite feldspathoid in which many tetrahedral silicon Si$^{4+}$ are substituted with intrinsic aluminum–chlorine defects, (vi) [ionoluminescence] IL at low temperature of all tectosilicate analyzed samples enhanced the 340 nm peak."
Sodalite has the formula Na$_4$Al$_3$Si$_3$O$_{12}$Cl.

## Lazurites

"Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: (Na,Ca)$_8$[(S,Cl,SO$_4$,OH)$_2$|(Al$_6$Si$_6$O$_{24}$)]. It is a feldspathoid and a member of the sodalite group. ... The colour is due to the presence of S$^{3-}$ anions. ... Lazurite is a product of contact metamorphism of limestone".
Lazurite (Lapis Lazuli) has the formula (Na,Ca)$_8$(Al,Si)$_{12}$O$_{24}$(S,So$_4$).

## Glaucophanes

Glaucophane is a mineral belonging to the amphibole group, chemical formula Na$_2$Mg$_3$Al$_2$Si$_8$O$_{22}$(OH)$_2$ The blue color is very diagnostic for this species. It, along with the closely related mineral riebeckite are the only common amphibole minerals that are typically blue. Glaucophane forms in metamorphic rocks that are either particularly rich in sodium or that have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone. This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. It is glaucophane's color that gives the blueschist facies its name. Glaucophane is also found in eclogites that have undergone retrograde metamorphism.
Glaucophane is an amphibole that has the formula Na$_2$(Mg,Fe$^{2+}$)$_3$Al$_2$Si$_8$O$_{22}$(OH)$_2$.

## Hibonites

Usually, "Hibonite ((Ca,Ce)(Al,Ti,Mg)$_{12}$O$_{19}$) is a brownish black mineral ... It is rare, but is found in high-grade metamorphic rocks on Madagascar. Some presolar grains in primitive meteorites consist of hibonite. Hibonite also is a common mineral in the Ca-Al-rich inclusions (CAIs) found in some [chondrite] chondritic meteorites. Hibonite is closely related to hibonite-Fe (IMA 2009-027, ((Fe,Mg)Al$_{12}$O$_{19}$)) an alteration mineral from the Allende meteorite. [Hibonite] is blue [perhaps like the image at left] in meteorite occurrence."
"Ti$^{3+}$ - Ti$^{4+}$ interactions are found in meteoritic minerals. A example of the blue color caused in some minerals by this interaction is the color of the fine-grained, titanium-containing, calcium aluminum oxide mineral, hibonite, in an inclusion known as the Blue Angel in the Murchison metorite. This mineral absorbs red light but lets blue light pass. The optical spectrum of this mineral has a band with a maximum absorption hear 690 nm. Better examples include blue hibonite in the Murray meteorite [image on the right] and the hibonite-bearing inclusions in the Vigarano CV3 chondrite meteorite."

## Spertiniites

Spertiniite has the chemical formula Cu(OH)$_2$.

## Calumetites

Calumetite has the chemical formula Cu(OH,Cl)$_2$·2H$_2$O.

## Lavendulans

Lavendulan has the chemical formula (Ca,Na)$_2$Cu$_5$(AsO$_4$)$_4$Cl·4-5H$_2$O.

## Zoisites

Tanzanite, a variety of zoisite that is purple-blue member of the epidote group.
Zoisite has the chemical formula Ca$_2$Al$_3$Si$_3$O$_{12}$OH.

## Linarites

Linarite is an monoclinic azure blue mineral with the chemical formula of PbCuSO$_4$(OH)$_2$.

## Spinels

On the right are some blue spinels from Baffin Island. Usually, spinel has the formula MgAl$_2$O$_4$. When Co$^{2+}$ substitutes for Mg$^{2+}$, the spinel (or cobalt spinel) is blue. In the formula this would be (Mg,Co)Al$_2$O$_4$.

## Aquamarines

On the right is a blue aquamarine (a variety of beryl) from the Tenente Ananias area, Rio Grande do Norte, Brazil.

## Halites

"Blue halite from Germany is the result of exposure to natural radiation. Initially, if halite (common salt) is exposed to gamma radiation, it turns amber because of F-centers. They are mostly electrons trapped at sites of missing Cl$^-$ ions. In time the electrons migrate to Na$^+$ ions and reduce it to Na metal. Atoms of Na metal, in turn, migrate to form colloidal sized aggregrates of sodium metal. They are the cause of the blue color."

## Hypotheses

* The origins of blue color in minerals may be as varied as the formation conditions of the minerals themselves.