Chemistry Reference
In-Depth Information
Mg
5
Al
2
Si
6
Al
2
Fe
5
Al
2
Si
6
Al
2
80
gedrite
60
orthorhombic
40
20
anthophyllite
cummingtonite
grunerite
monoclinic
Mg
7
Si
8
20
20
40
80
Fe
7
Si
8
Figure 3.18
Ferro-magnesian amphiboles (after Tröger, 1961).
Katophorite
Si
7
Al
riebeckite
glaucophane
richterite
Si
8
R
3+
tremolite
1
2
3
Figure 3.19
Sodi-calcic and sodic amphiboles.
Sodic amphiboles
Sodic amphiboles, whose X site is occupied by sodium, form two groups:
glaucophane-riebeckite series, whose intermediate terms are called cros-
sites, are high pressure metamorphic minerals. Glaucophane is equiva-
lent to the association chlorite
+
albite;
riebeckite-arfvedsonite-eckermannite series. The pure eckermannite
end member does not exist in the nature, natural eckermannite still con-
taining some calcium. These are mineral acidic or intermediate alkaline
igneous rocks, saturated in silica or not.
