# Chemicals/Sulfurs

Native sulfur is a naturally occurring chalcogen mineral. On Io native sulfur occurs in yellow and red allotropes.

## Molecules

Sulfur forms several polyatomic molecules. The best-known allotrope is octasulfur, cyclo-S $_8$. The point group of cyclo-S $_8$ is D $_{4d}$ and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless, but impure samples have an odor similar to that of matches. It melts at 115.21 °C (239.38 °F), boils at 444.6 °C (832.3 °F) and sublimates easily. At 95.2 °C (203.4 °F), below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-polymorph. The structure of the S $_8$ ring is virtually unchanged by this phase change, which affects the intermolecular interactions. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from β-octasulfur to γ-sulfur, again accompanied by a lower density but increased viscosity due to the formation of polymers. At higher temperatures, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above 200 °C (392 °F). The density of sulfur is about 2 g/cm$^3$, depending on the allotrope; all of the stable allotropes are excellent electrical insulators.

## Gases

A strong odor called "smell of sulfur" actually is given off by several sulfur compounds, such as hydrogen sulfide and organosulfur compounds.

## Solids

Sulfur forms over 30 solid allotropes, more than any other element.

## Minerals

Sulfur has 23 known isotopes, four of which are stable: $^{32}$S (94.99±0.26 %), $^{33}$S (0.75±0.02 %), $^{34}$S (4.25±0.24 %), and $^{36}$S (0.01±0.01 %). Other than $^{35}$S, with a half-life of 87 days and formed in cosmic ray spallation of $^{40}$Ar, the radioactive isotopes of sulfur have half-lives less than 3 hours.
When sulfide minerals are precipitated, isotopic equilibration among solids and liquid may cause small differences in the δ$^{34}$S values of co-genetic minerals. The differences between minerals can be used to estimate the temperature of equilibration. The δ$^{13}$C and δ$^{34}$S of coexisting carbonate minerals and sulfides can be used to determine the pH and oxygen fugacity of the ore-bearing fluid during ore formation.

## Arsenopyrites

Arsenopyrite (FeAsS) on the right is 33.3 at % arsenic.

## Cinnabars

Cinnabar or cinnabarite (red mercury(II) sulfide (HgS), native vermilion), is the common ore of mercury. Its color is cochineal-red, towards brownish red and lead-gray. Cinnabar [may be] found in a massive, granular or earthy form and is bright scarlet to brick-red in color. Generally cinnabar occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs. Cinnabar is deposited by epithermal ascending aqueous solutions (those near surface and not too hot) far removed from their igneous source.

## Covellites

Covellite is a copper sulfide (CuS) mineral.
Covellite 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.

## Galenas

Galena in the image on the right is the metallic cuboidal crystal atop a matrix. Galena is PbS, 50 atomic % lead and 50 atomic % sulfur. Each cubic unit cell contains four PbS molecules in a face-centered cubic lattice.

## Millerites

Millerite is a nickel sulfide mineral, NiS. Millerite is a common metamorphic mineral replacing pentlandite within serpentinite ultramafics. It is formed in this way by removal of sulfur from pentlandite or other nickeliferous sulfide minerals during metamorphism or metasomatism.

## Pentlandites

This massive sulfide specimen on the right consists of brassy gray-brown pyrrhotite (Fe $_{(1-x)}$S - imperfect iron monosulfide) with brighter brassy-colored patches of pentlandite ((Ni,Fe) $_9$S $_8$ - nickel iron sulfide), plus a network of grayish to black patches of magnetite (Fe $_3$O $_4$ - iron oxide).
Pentlandite is an iron–nickel sulfide with the chemical formula (Fe,Ni) $_9$S $_8$. Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of weight.

## Realgars

Realgar an arsenic sulfide mineral of 1.5-2.5 Mohs hardness is used to make red-orange pigment.
Realgar is a sulfide mineral. But, with equal atomic numbers of sulfur and arsenic, it may act as a pnictide.
This piece on the right is from the less well-known Royal Reward Mine of Washington.

## Troilites

Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe$_{(1-x)}$S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency which gives pyrrhotite its characteristic magnetism, troilite is non-magnetic.
Troilite can be found as a native mineral on Earth but is more abundant in meteorites, in particular, those originating from the Moon and Mars. It is among the minerals found in samples of the Chelyabinsk meteor (the meteorite that struck Russia in Chelyabinsk on February 15th, 2013). Uniform presence of troilite on the Moon and possibly on Mars has been confirmed by the Apollo, Viking and Phobos space probes. The relative intensities of isotopes of sulfur are rather constant in meteorites as compared to the Earth minerals, and therefore troilite from Canyon Diablo meteorite is chosen as the international sulfur isotope ratio standard, the Canyon Diablo Troilite (CDT).
Troilite has hexagonal structure (Pearson symbol hP24, Space group P-62c No 190). Its unit cell is approximately a combination of two vertically stacked basic NiAs-type cells of pyrrhotite, where the top cell is diagonally shifted. For this reason, troilite is sometimes called pyrrhotite-2C.
A meteorite fall was observed in 1766 at Albareto, Modena, Italy. Samples were collected and studied by Domenico Troili who described the iron sulfide inclusions in the meteorite. These iron sulfides were long considered to be pyrite (i.e., FeS $_2$). In 1862, German [mineralogist Gustav Rose analyzed the material and recognizd it as stoichiometric 1:1 FeS andgave it the name troilite in recognition of the work of Domenico Troili.
Troilite has been reported from a variety of meteorites occurring with daubréelite, chromite, sphalerite, graphite, and a variety of phosphate and silicate minerals. It has also been reported from serpentinite in the Alta mine, Del Norte County, California and in layered igneous intrusions in Western Australia, the Ilimaussaq intrusion of southern Greenland, the Bushveld Complex in South Africa and at Nordfjellmark, Norway. In the South African and Australian occurrence it is associated with copper, nickel, platinum iron ore deposits occurring with pyrrhotite, pentlandite, mackinawite, cubanite, valleriite, chalcopyrite and pyrite.
Troilite is extremely rarely encountered in the Earth's crust (even pyrrhotite is relatively rare compared to pyrite and Iron(II) sulfate minerals). Most troilite on Earth is of meteoritic origin. One iron meteorite, Mundrabilla contains 25 to 35 volume percent troilite. The most famous troilite-containing meteorite is Canyon Diablo. Canyon Diablo Troilite (CDT) is used as a standard of relative concentration of different isotopes of sulfur. Meteoritic standard was chosen because of the constancy of the sulfur isotopic ratio in meteorites, whereas the sulfur isotopic composition in Earth materials varies due to the bacterial activity. In particular, certain sulfate reducing bacteria can reduce $^{32}$ SO$^{2−}$ $_4$ 1.07 times faster than $^{34}$ SO$^{2−}$ $_4$, which may increase the $^{34}$ S/$^{32}$ S ratio by up to 10%.
Troilite is the most common sulfide mineral at the lunar surface. It forms about one percent of the lunar crust and is present in any rock or meteorite originating from moon. In particular, all basalts brought by the Apollo 11, Apollo 12, Apollo 15 and Apollo 16 missions contain about 1% of troilite.
Troilite is regularly found in Martian meteorites, similar to the Moon's surface and meteorites, the fraction of troilite in Martian meteorites is close to 1%.
Based on observations by the Voyager spacecraft in 1979 and Galileo in 1996, troilite might also be present in the rocks of Jupiter’s satellites Ganymede and Callisto. Whereas experimental data for Jupiter's moons are yet very limited, the theoretical modeling assumes large percentage of troilite (~22.5%) in the core of those moons.
* Category: Sulfide mineral.
* Formula: FeS.
* System: Hexagonal crystal system.
* Class: Ditrigonal dipyramidal (6m2) H-M symbol: (6m2).
* Symmetry: P62c.
* Unit cell: a = 5.958, c = 11.74 [Å]; Z = 12.
* Color: Pale gray brown.
* Habit: Massive, granular; nodular; platey to tabular.
* Cleavage: None.
* Fracture: Irregular.
* Mohs hardness: 3.5 - 4.0.
* Luster: Metallic.
* Streak: Gray black.
* Diaphaneity: Opaque.
* Gravity: 4.67–4.79.
* Alteration: Tarnishes on exposure to air.

## Glaciology

"Both sulfur and oxygen isotopes of sulfate preserved in ice cores from Greenland and Antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods."

## Resources

* Chemicals/Actinides
* Chemicals/Aluminums
* Chemicals/Berylliums
* Chemicals/Leads
* Chemicals/Lithiums
* Chemicals/Nickels
* Chemicals/Thoriums