ERTH 2002

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ERTH 2002

• Mineral of the Week (MoW)
• olivine
• 2. pyroxene
• 3. feldspar (some review)
• 4. garnet
• 5. amphibole
• 6. mica
• 7. quartz
• 8. clays
• 9. carbonates (some review)
• 10. Fe-Ti oxides
• 11. sulphides (some review)

properties chemical composition crystal
structure phase diagrams occurrence use
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)

photos mindat.org
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2 where A Na,K X
Ca,Na,Fe,Mg Y Mg,Fe,Mn,Al T Al,Si root
formula tremolite Ca2Mg5Si8O22(OH)2
several different families of amphibole can be
recognised depending on X-site occupancy
calcic amphiboles X mostly Ca (e.g.,
actinolite, hornblende) sodic amphiboles X
mostly Na (e.g., glaucophane) Fe-Mg amphiboles X
mostly Fe,Mg (e.g., anthophyllite)
(ortho-) (etc...)
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
TOT groups linked by other cations (A, X)
A
SiO44- double chain (T-site)
chains linked by octahedral Y-sites (M1, M2)
I-beam
T O T
relationship between structure and cleavage
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
biaxial ve mod biref pale green
biaxial ve or ve mod biref green to brown
act hbl
interference colour range
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
clear distinction among various amphibole
groups requires working out pleochroic scheme
biaxial ve or ve mod biref green to brown
biaxial ve mod biref pale green
act hbl
interference colour range
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
ERTH 3020 samples
PCA-03 anthophyllite (Fe-Mg
orthoamphibole) (PPL, 2.5 mm)
BVA-02 blue-green hornblende (PPL, 6 mm)
OM-5 pleochroism in Ti-rich hornblende
(kaersutite) (PPL, 4 mm) ERTH 2001
1513 glaucophane (sodic amphibole) (PPL, 6
mm)
Q45A green hornblende (PPL, 6 mm)
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MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
occurrence ubiquitous in metabasites (type
of amphibole varies with bulk composition and
metamorphic grade) common in intermediate
orthogneisses common in marbles and
meta-ultramafites common in intermediate and
alkaline igneous rocks (andesites, diorites,
lamprophyres, etc) common accessory mineral
in mantle peridotites use fibrous
varieties have been used for asbestos
(anthophyllite, crocidolite fibrous
riebeckite) more carcinogenic than asbestiform
serpentine (chrysotile)!!! some use as
dimension (decorative) stone