Science Fair Project Encyclopedia
|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.|
|Hardness||2 - 2.5|
|Luster||Vitreous, pearly, dull|
|Streak||Pale green to grey|
|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.
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.
References and external links
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