Chlorite group of minerals

Chlorite group of minerals

1. Seminar On Chlorite group of minerals

2. Contents Introduction Chlorite structure Physical properties Members of chlorite group Distinguishing from other minerals Occurence Economic importance Conclusion

3. INTRODUCTION The  chlorites  are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn.

4. Contd… In addition, zinc, lithium, and calcium species are known. The great range in composition results in considerable variation in physical, optical, and  X-ray  properties. Similarly, the range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks,  hydrothermal  rocks and deeply buried sediments . The most common species in the chlorite group are  clinochlore  and  chamosite .

5. CHL0RITE STRUCTURE The typical general formula is: ( Mg,Fe ) 3 ( Si,Al ) 4 O 10 (OH) 2 · ( Mg,Fe ) 3 (OH) 6 . This formula emphasises the structure of the group. Chlorites have a 2:1 sandwich structure (2:1 sandwich layer =  t etrahedral- o ctahedral- t etrahedral =  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 composed of (Mg 2+ , Fe 3+ )(OH) 6 . This (Mg 2+ , Fe 3+ )(OH) 6  unit is more commonly referred to as the  brucite -like layer, due to its closer resemblance to the mineral brucite (Mg(OH) 2 ). 

6. colour greenish black to white Luster vitreous to pearly Diaphaneity transparent to translucent Cleavage Basal(001), perfect Mohs Hardness 2 - 2.5 Specific Gravity 2.6 - 3.3 Distinguishing Characteristics Color, various shades of green, yellow, white, pink, rose-red Streak greenish to colourl ess Crystal System Monoclinic

7. Optical properties Refractive indices increase with increasing Fe and Al contents. Fe-rich chlorites are biaxial negative. Mg-rich chlorites are negative. The sign of elongation of chlorites is opposite to the optic sign and is much easier to obtain, especially in fine-grained examples. Pleochroism strengthens with Fe content. Mn chlorite – orange-brown; Nickel – yellow/green; Chromium – pinks/violet. For the most part, mildly pleochroic with 1st order grey birefringence. Anomalous colours include browns (Mg-rich) and violet-blues

8. MEMBERS OF CHLORITE GROUP Baileychlore Borocookeite Chamosite Clinochlore Cookeite Corundophilite Franklinfurnaceite Nimite Orthochamosite Pennantite Sudoite

9. Distinguishing From Other Minerals Chlorite is so soft that it can be scratched by a finger nail. The powder generated by scratching is green. It feels oily when rubbed between the fingers. The plates are flexible, but not elastic like mica. Talc is much softer and feels soapy between fingers. The powder generated by scratching is white. Mica plates are elastic whereas chlorite plates are flexible without bending back

10. OCCURRENCE Chlorite is commonly found in igneous rocks as an alteration product of mafic minerals such as pyroxene, amphibole, and biotite. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a metasomatism product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with hydrothermal ore deposits and commonly occurs with epidote, sericite, adularia and sulfide mineralswith talc.

11. Contd … . Chlorite is also a common metamorphic mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of lower greenschist facies. It occurs in the quartz, albite, sericite, chlorite, garnet assemblage of pelitic schist. Within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association

12. PROCHLORITE (Ripidolite) Composition-H4Mg3Si2O9 Crystal System - Monoclinic Habit –massive foliated or granular Hardness 1-2 Specific gravity-2.78-2.98 Translucent to opaque Colour-green, olivine green blakish green Pleochroism-distinct Occurence-clorite schist other metamophic rock,serpentine Common through out alps,switserland,rauris in salsberg.

13. CLINOCHLORE Composition –H 8 Mg5 Al2 Si3 O18 System- monoclinic Cleavege-perfect Hardness 2-2.5 Sp gravity 2.65-2.78 Colour -pale green to yellowish and white Diaphinity –transparent to transulasent Occurance with chloritic or schists and with serpentine. found in mussa alps in alla valley zermat in valis,foster iron mine newyork

14. CLINOCHLORE

15. PENNINITE Apparantly rhombohedral in form butsrctly suedo rhombohedral and monoclinic shows highly prefect cleavege Hardness -2-2.5 Specific gravity -2.6-2.85 Lusture –pearly Clour –emarald to olivine green also violet pink transparent to subtraslusent Distinct pleochroism Occures in valais switserland with serpentine, from the alla valley in pidmont with clinoclore also with clorite at various point in north carolina.

16. PENNINITE

17. CHAMOSITE Composition-15(Fe,Mg)O.5Al2O3.11SiO2.16H2O Habit-Compact or oolitic Hardness-3 Specific gravity-3-3.4 Colour-greenish grey to black Occurence-with various ore deposits,with sphallerite,galena,pyrite,siderite etc Forms thick bed of limited extent in limestone at rhone valley,valais.With iron carbonate at scheimeilfield

18. ECONOMIC IMPORTANCE Used to extract chlorine Used as gemstone

19. CONCLUSIONS Minerals of chlorite group are mainly products of low temperatures and mainly of hydrothermal or low temperature genesis. They also occur as products of transformation of ferromagnesian minerals-biotite,amphibole, pyroxene and others in amphibolite rocks. Analyzing different varieties of amphibolite rocks, it is represented that genesis of chlorite in them is often followed with complex processes of mineral genesis, where beside chlorite, created were other secondary minerals like prenite, epidotite, clinocoisite, serpentine, spinel,especially zeolitic. Also, occurrence of chlorite together with appropriate minerals is important because on th basis of this mineral association we can determine affiliation to metamorphic facies.

20. References Rock forming minerals- ZUSSMAN DANA’s text book of mineralogy-W.E. FORD www.wikipedia.com/chloritegroup.htm www.geology.com/chloriteminerals

21. Thank you