Aguilarite
| Aguilarite | |
|---|---|
|
Aguilarite - San Carlos Mine, La Luz, Guanajuato municipality, Mexico. Specimen height is 3.9 cm. | |
| General | |
| Category | Sulfosalt minerals |
| Formula (repeating unit) | Ag4SeS |
| Strunz classification | 2.BA.55 |
| Dana classification | 2.4.1.3 |
| Crystal symmetry | Space group: P21/n[1] |
| Unit cell |
a=4.2478(2) Å, b=6.9432(3) Å c=8.0042(5) Å, β=100.103(2)º Z=4[1] |
| Identification | |
| Color | Bright lead-gray on fresh surfaces; dull iron-black on exposure to air. |
| Crystal system | Monoclinic[1] |
| Cleavage | None observed |
| Fracture | Hackly |
| Tenacity | Sectile |
| Mohs scale hardness | 2.5[2] 1–1.5[1] |
| Luster | Metallic |
| Streak | Gray-black |
| Diaphaneity | Opaque |
| Ultraviolet fluorescence | Non-fluorescent[3] |
| References | [2] |
Aguilarite is an uncommon sulfosalt mineral with formula Ag4SeS. It was described in 1891 and named for discoverer Ponciano Aguilar.
Description
Aguilarite is bright lead-gray on fresh surfaces but becomes dull iron black when exposed to air.[2] The mineral occurs with massive habit, as elongated pseudododecahedral crystals up to 3 centimetres (1.2 in), or as intergrowths with acanthite or naumannite.[4]
Discovery
In the late 19th century, Ponciano Aguilar, superintendent of the San Carlos mine in Guanajuato, Mexico, found several specimens of a mineral thought to be naumannite.[4][5] The samples were given to F. A. Genth for identification, who, along with S. L. Penfield, discovered that it was a new mineral. The mineral was described in the American Journal of Science in 1891 and named aguilarite in honor of Ponciano Aguilar.[5] When the International Mineralogical Association was founded, aguilarite was grandfathered as a valid mineral species.[6]
Occurrence
Aguilarite is uncommon, and forms at relatively low temperatures in hydrothermal deposits rich in silver and selenium but deficient in sulfur.[4] The mineral is known from a number of countries in North and South America, Europe, Asia, and Australasia.[2][4] Aguilarite occurs in association with acanthite, calcite, naumannite, pearceite, proustite, silver, stephanite, and quartz.[4]
Chemistry and structure
In 2013, aguilarite's chemistry and crystal structure were reexamined by Bindi and Pingitore.[1] The significant reevaluation of aguilarite did not discredit its status as a valid mineral, but it was established as the selenium analogue of acanthite instead of sulfur-rich naumannite.[7] The sample primarily studied came from the Gem and Mineral Collection of the Department of Geosciences at Princeton University.[8]
The work of Petruk et al. in 1974 formed the basis of knowledge regarding the silver–sulfur–selenium system for about forty years. They indexed their x-ray diffraction patterns of aguilarite on an orthorhombic cell similar to naumannite.[9] Bindi and Pingitore determined that aguilarite is, in fact, monoclinic and is isostructural to acanthite and not naumannite.[1] Bindi and Pingitore believe that Petruk et al. were unable to resolve closely spaced peaks due to low resolution equipment, making aguilarite appear similar to naumannite. Additionally, a number of inconsistencies in unit cell dimensions in the 1974 work show that aguilarite does not have the same structure as naumannite.[10]
The crystal structure of aguilarite consists of planes nearly parallel to (010) composed of tetrahedrally coordinated nonmetal atoms and AgX3 triangles (where X is a nonmetal). The planes are joined by twofold-coordinated silver atoms.[11]
Aguilarite is part of the acanthite-like solid solution series Ag2S–Ag2S0.4Se0.6. The mineral comprises the range from 50 atomic percent selenium up to the transition from monoclinic to orthorhombic.[7]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Bindi & Pingitore 2013, p. 21.
- ↑ 2.0 2.1 2.2 2.3 "Aguilarite". Mindat. Retrieved January 20, 2013.
- ↑ "Aguilarite". Webmineral. Retrieved March 11, 2013.
- ↑ 4.0 4.1 4.2 4.3 4.4 Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Aguilarite" (PDF). Handbook of Mineralogy. Chantilly, VA: Mineralogical Society of America.
- ↑ 5.0 5.1 Genth 1891, p. 401.
- ↑ "The New IMA List of Minerals – A Work in Progress – Update: November 2012" (PDF). Commission on New Minerals, Nomenclature and Classification. International Mineralogical Association. p. 3. Retrieved January 20, 2013.
- ↑ 7.0 7.1 Bindi & Pingitore 2013, p. 30.
- ↑ Bindi & Pingitore 2013, p. 23.
- ↑ Bindi & Pingitore 2013, p. 22.
- ↑ Bindi & Pingitore 2013, p. 29.
- ↑ Bindi & Pingitore 2013, p. 26.
- Bibliography
- Bindi, L.; Pingitore, N. E. (February 2013). "On the symmetry and crystal structure of aguilarite, Ag4SeS". Mineralogical Magazine 77 (1): 21–31. doi:10.1180/minmag.2013.077.1.03. (subscription required)
- Genth, F. A. (1891). Dana, James D.; Dana, Edward S., eds. "Aguilarite, a new species". American Journal of Science 141 (241–246).
Further reading
- Petruk, W.; Owens, D. R.; Stewart, J. M.; Murray, E. J. (August 1974). "Observations on acanthite, aguilarite and naumannite" (PDF). The Canadian Mineralogist 12 (6): 365–369.
External links
Media related to aguilarite at Wikimedia Commons