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)4O10(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 = 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
composed of (Mg2+, Fe3+)(OH)6. This
(Mg2+, Fe3+)(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 colourless
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

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

10. 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

11. 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.


12. 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

13. 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.

14. CLINOCHLORE
 Composition –H8 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

15. CLINOCHLORE

16. 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.

17. PENNINITE

18. 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

19. ECONOMIC IMPORTANCE
 Used to extract chlorine
 Used as gemstone

20. 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.

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

22. Thank you