Calcic amphiboles

2.  INTRODUCTION
 AMPHIBOLE GROUP
 CALCIC AMPHIBOLES
 STRUCTURE
 CHEMISTRY
 PHYSICAL AND OPTICAL PROPERTIES
 PARAGENESIS
 CONCLUSIONS
 REFERENCES

3.  The Amphiboles are a group of hydroxylated chain
silicates (inosilicates) with some substitutions of F and
Cl for (OH).
 They include both Monoclinic and Orthorhombic
members.
 There are three main groups
(a) Ca-poor amphiboles
(b) Ca-rich amphiboles
(c) Alkali amphiboles

4. The essential feature of the structures of all
amphiboles is the presence of (Si,Al)O4
tetrahedra linked to form chains which have
double the width of those in pyroxenes and
have the composition (Si4O11)n.
The double chains or bands repeat along their
length.

8.  The amphibole structure admits great flexibility of
ionic replacement, and the minerals of the group
exhibit an extremely wide range of chemical
composition.
 The general formula of the amphiboles can be
expressed as
X2-3Y5Z8O22(OH)2
X=Ca, Na, K, Mn
Y=Mg,Fe+3,Fe+2,Al,Ti;Mn,Cr,Li,Zn
Z=Si, Al

10.  They are monoclinic.
 Include Tremolite-ferroactinolite, and the common
hornblendes.
 General formula is
AX2Y5Z8O22(OH,F)2
A=Na ;X=Ca ;Y=Mg,Fe,Al ;Z=Si or Al

11. CHEMISTRY
Ca2(Mg,Fe+2)5(Si8O22)(OH,F)2
Replacement of Mg by Fe and Si by Al

13. PHYSICAL AND OPTICAL PROPERTIES
 2V 86-65 degree
 OAP (010)
 Dispersion:weak
 D:3.02-3.44 H:5-6
 Cleavage:good(110)
 Twinning:simple
 Colour:Tremolite colourless or grey , actinolite pale to
dark green
 Pleochroism: tremolite non-pleochroic ; actinolite and
ferroactinolite showing pleochroism

14. DISTINGUISHING FEATURES
 Negative optical character
 Low refractive indices
 Straight extinction
 Higher birefringence
PARAGENESIS
 Tremolite and actinolite are metamorphic minerals.
Occur in both contact and regionally metamorphosed
rocks .
 In thermally metamorphosed impure dolomites ,
tremolite forms by reaction between dolomite and
quartz

15. 5CaMg(CO3)2+8SiO2+H2O→Ca2Mg5Si8O22(OH)2+3Ca
CO3+7CO
 At higher grade of metamorphism tremolite is unstable
and if quartz is available it reacts with calcite to form
diopside
Ca2Mg5Si8O22(OH)2+3CaCO3+2SiO2→5CaMgSi2O6+3
CO2+H2O

16.  If there is an excess of dolomite the tremolite reacts
with dolomite and give forsterite and calcite
Ca2Mg5Si2O22(OH)2+11CaMg(CO3)2→8Mg2SiO4+13
CaCO3+9CO2+H2O
 Tremolite and actinolite also occur in regionally
metamorphosed carbonate rocks and they are
characteristic minerals in low grade regionally
metamorphosed ultrabasic rocks.

17. CHEMISTRY
(Na,K)0-1Ca2(Mg,Fe+2,Fe+3,Al)5(Si6-7Al2-1O22)(OH,F)2
 The hornblende series or common hornblendes is the
name given to any amphibole which has a composition
occurring in a field of composition which is itself defined
by four end-members

18. Hastingsite Ca2(Mg4Al)(Si7AlO22)(OH,F)2
Tschermakite Ca2(Mg3Al2)(Si6Al2O22)(OH,F)2
Edenite NaCa2Mg5(Si7AlO22)(OH,F)2
Pargasite NaCa2(Mg4Al)(Si6Al2O22)(OH,F)2

19. PHYSICAL AND OPTICAL PROPERTIES
 2V 95-27 degree
 D: 3.02-3.45
 H: 5-6
 Cleavage : good(110)
 Twinning:simple(100),lamellar
 Colour:black to greenish black
 Pleochroism:variable in greens,yellow-green,bluish
green and brown
 OAP:parallel to (010)

21. DISTINGUISHING FEATURES
 Higher refractive indices
 Moderate to strong pleochroism
 Optic axial angle and extinction angle
PARAGENESIS
 Minerals of intermediate and some acid plutonic
igneous rocks.
 They are essential constituents of amphibolite facies of
regional metamorphism.
 Tschermakite occurs in high-grade metamorphic rocks
and pargasite in metamorphosed impure dolomitic
limestones.

22. (Ca,Na)2-3(Mg,Fe+2)3-2(Fe+3,Al)2-3O2(Si6Al2O22)
 OAP:parallel to (010)
 Cleavage:perfect
 Twinning:simple,lamellar
 D:3.19-3.30 , H:5-6
 Colour:brown to black
 Pleochroism:pale yellow,yellow
 Occur in volcanic rocks and they are constituents of
andesites and latites

23. Ca2(Na,K)(Mg,Fe+2,Fe+3)4Ti(Si6Al2O22)(O,OH,F)2
 OAP:parallel to (010)
 D:3.2-3.28 , H:5-6
 Cleavage:perfect(110)
 Twinning:simple,lamellar
 Colour:dark brown to black
 A typical constituent of alkaline volcanic rocks and
occurs as phenocrysts in trachybasalts

24. Ca2(Na,K)(Fe+2,Mg,Fe+3,Mn)5(Si6.5Al1.5O22)(OH)2
 . OAP:parallel to (010)
 D:3.35-3.44 , H:5-6
 Cleavage:prfect(110)
 Twinning:simple(100)
 Colour:black
 Paragenesis is restricted to alkaline rocks,and it occurs
in theralites,essexites,nepheline-syenite.

25. The amphibole are a group of hydroxylated
chain silicates with some substitution of F and
Cl for (OH).
Three main groups are there (a)Ca-poor
amphiboles;(b)Ca-rich amphiboles;(c)alkali
amphiboles.
The Ca-rich amphiboles (Ca>Na) are
monoclinic.

26. They include tremolite-ferroactinolite , and the
common hornblendes(the hornblende group of
minerals).
Members of the amphibole group of minerals
occur in a wide range of P,T-environments and
are common constituents of both igneous and
metamorphic rocks.
Amphiboles occur characteristically in the
plutonic rocks and in general are relatively
unimportant minerals of volcanic rocks.

27.  W.A.DEER, R.A.HOWIE, J.ZUSSMAN (1965)
,Textbook Of Mineralogy ,p.148-178.
 WWW.Wikipedia.org/wiki/amphibole.

28. THANK YOU...