Cummingtonite

MINERALS INDEX

Amphibole Group

Arseniosiderite

Calcium larsenite

Chlorophoenicite

Chysolite Group

Ferroschallerite

Friedelite Group

Hydrohetaerolite

Leucophoenicite

Magnesium- chlorophoenicite

Native Elements

Phosphates, Arsenates and Vanadates

Serpentine Group

Sulphides and Arsenides

Tremolite and Actinolite

Unconfirmed Species

Zinc schefferite

Cummingtonite

An analysis of an amphibole found at Franklin, long called actinolite because of external resemblance to that variety, has shown that it is really a zinc-manganese cummingtonite having the formula given on page 70, the molecular ratio of MgO : FeO : MnO : ZnO being approximately 3 : 3 : 3 : 2. The specific gravity is 3.44.

**Analysis of cummingtonite**
(L. H. Bauer (273), analyst)
SiO₂	49.74
Al₂O₃	1.72
FeO	12.80
MgO	8.31
ZnO	10.46
MnO	13.79
CaO	0.49
Na₂O	0.22
H₂O	2.16
	99.69

The mineral forms large green prismatic crystals with a cleavage angle m /\ m' = 54° 28', embedded in rhodonite or garnet, in one specimen in feldspar, and accompanied by ferroschallerite.

This variety of cummingtonite is optically biaxial and negative; 2V = 75° ±2° ; Z /\ c = 15° ; Y = b; a = 1.657, b = 1.674, g = 1.685.


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