Chlorite group
From Biocrawler, the free encyclopedia.
| Chlorite group | |
|---|---|
 | |
| General | |
| Category | Mineral group |
| Formula | (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6 |
| Identification | |
| Colour | Various shades of green; rarely yellow, red, or white. |
| Habit | Foliated masses, scaley aggregates, disseminated flakes. |
| System | Monoclinic 2/m; with some triclinic polymorphs. |
| Cleavage | Perfect 001 |
| Fracture | Lamellar |
| Hardness | 2 - 2.5 |
| Luster | Vitreous, pearly, dull |
| RI | 1.57 -1.67 |
| Pleochroism | |
| Streak | Pale green to grey |
| SG | 2.6-3.3 |
| Fusibility | |
| Solubility | |
| Other | Folia flexible - not elastic |
Chlorite is a group of phyllosilicate minerals often classified as clays. Chlorites have a 2:1 sandwich structure (2:1 sandwich layer = tetrahedral-octahedral-tetrahedral = t-o-t...), this is often referred to as a talc layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space (the space between each 2:1 sandwich filled by a cation) is comprised of (Mg2+, Fe3+)(OH)6. The layer (Mg2+, Fe3+)(OH)6 is more commonly referred to as the brucite-like layer, due to its closer resemblance to the mineral brucite (Mg(OH)2). Therefore, chlorite's structure appears as follows: -t-o-t-brucite-t-o-t-brucite...
The typical general formula is: (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6. The great range in composition results in considerable variation in physical, optical, and X-ray properties.
The name is from the Greek chloros, meaning "green", in reference to its color.
| Contents |
Occurrence
Chlorite is commonly found in igneous rocks as an alteration product of mafic minerals such as pyroxenes, amphiboles, and biotite. It is a common alteration mineral associated with hydrothermal ore deposits and commonly occurs with epidote. Chlorite is a common metamorphic mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of the greenschist facies. Occurs in quartz, albite, sericite, chlorite, garnet assemblage of pelitic schist.
Members of the Chlorite group:
- Amesite (Mg,Fe)4Al4Si2O10(OH)8
- Baileychlore (Zn,Fe+2,Al,Mg)6(Al,Si)4O10(O,OH)8
- Chamosite (Fe,Mg)3Fe3AlSi3O10(OH)8
- Clinochlore (kaemmererite) (Fe,Mg)3Fe3AlSi3O10(OH)8
- Cookeite LiAl5Si3O10(OH)8
- Corundophilite (Mg,Fe,Al)6(Al,Si)4O10(OH)8
- Daphnite (Fe,Mg)3(Fe,Al)3(Al,Si)4O10(OH)8
- Delessite (Mg,Fe+2,Fe+3,Al)6(Al,Si)4O10(O,OH)8
- Gonyerite (Mn,Mg)5(Fe+3)2Si3O10(OH)8
- Nimite (Ni,Mg,Fe,Al)6AlSi3O10(OH)8
- Odinite (Al,Fe+2,Fe+3,Mg)5(Al,Si)4O10(O,OH)8
- Orthochamosite (Fe+2,Mg,Fe+3)5Al2Si3O10(O,OH)8
- Penninite (Mg,Fe,Al)6(Al,Si)4O10(OH)8
- Pannantite (Mn,Al)6(Al,Si)4O10(OH)8
- Rhipidolite (prochlore) (Mg,Fe,Al)6(Al,Si)4O10(OH)8
- Sudoite (Mg,Fe,Al)4-5(Al,Si)4O10(OH)8
- Thuringite (Fe+2,Fe+3,Mg)6(Al,Si)4O10(O,OH)8
Clinoclore, penninite, and chamosite are the most common varieties.
See also
References and external links
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0471805807
- Mineral Galleries (http://mineral.galleries.com/minerals/silicate/chlorite/chlorite.htm)
- Mindat.org (http://www.mindat.org/min-1016.html)
- Chlorite - Maricopa edu (http://www.gc.maricopa.edu/earthsci/imagearchive/chlorite.htm)
