|ASTROPHYLLITE CRYSTALS FROM SAINT PETERS DOME AREA, PIKES PEAK MASSIF. WIDTH OF SPECIMEN IS ~2.2 CM.|
Astrophyllite is another one of those minerals that would have never popped into my mind if not for a move to Colorado Springs. Somehow I don’t remember anything about this mineral from my basic mineralogy class; however, that was decades ago and much of that class information seems lost in the deep recesses of my mind! I certainly never saw the mineral in Kansas, or Missouri, or Wisconsin (my other homes). But, in exploring around the Pikes Peak Massif near Colorado Springs I heard about this brass- to golden-colored bladed mineral that was found in some of the pegmatites and “granites”. I guess the name, “star leaf”, comes from the fact that at some localities the mineral occurs as “star bursts or rosettes”; however, all of the Colorado specimens that I have seen are rather bladed or tabular, soft (~3 on Mohs scale), some perfect basal cleavage, and sort of a greasy luster. It really doesn’t look like much of any mineral that I observed previously except perhaps phlogopite. However, this mica has cleavage plates that are transparent and flexible. Astrophillite plates are brittle and opaque.
Astrophyllite is a rather complex mineral, at least to me, a hydrous potassium sodium iron titanium silicate: (K,Na)3(Fe,Mn)7Ti2Si8O24(O,OH)7. I’m just glad that chemical formula was never on a test!
|Astrophyllite acquired at Tucson, 2014. Collected from the Khibiny Massif, Kola peninsula, Russia. Note the golden-orange chatoyancy of some crystals. i presume the matrix is something like albite. Width of specimen ~5cm.|
GOLDEN BLADES OF ASTROPHYLLITE FROM SAINT PETERS DOME. WIDTH OF SPECIMEN IS ~2.5 CM.
Eckel, E. B. et al, 1997, Minerals of Colorado: Denver Museum of nature and Science and Fulcrum Publishing, Denver.