babingtonite

[From Dr. Babbington.]
(Min.) A mineral occurring in triclinic crystals approaching pyroxene in angle, and of a greenish black color. It is a silicate of iron, manganese, and lime.

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Environment

A late, probably hydrothermal (hot-water), secondary mineral, commonly associated in traprock with the zeolites, and on joint surfaces in dark plutonics or gneiss.

Tiny crystals usually very brilliant. Roughly equidimensional, with zeolite-surrounded faces striated. Always in crystals.

Black. Luster glassy; hardness 5Ɖ-6; specific gravity 3.4; fracture conchoidal; cleavage 2 pinacoidal (1 good) at 87° and 93°. Translucent as thin splinters. Grains under the polarizing microscope are colorful and beautifully pleochroic.

Alkaline calcium iron silicate (about 19% CaO, 29% FeO plus Fe ₂ O ₃ , 51.5% SiO ₂ , and 0.5% H ₂ O, often with some manganese).

Fuses easily to a black magnetic globule. Insoluble in hydrochloric acid.

In appearance and in the hand, it might be rather difficult to distinguish from some of the black pyroxenes, but is less prismatic than the amphiboles usually are. The easy melting and the magnetism are helpful; but most of all, one relies on the mineral associates and the paragenesis. Typically perched on prehnite.

An attractive but uncommon mineral of seams and silicate veins, found best at several quarry localities in Massachusetts. Once, at a quarry in Blueberry Hill, Woburn, Massachusetts, in crevices in a diorite, with sphene, calcite and thin-bladed crystals of prehnite. Small ones uncovered by dissolving away the calcite are very brilliant and unmistakable. Larger crystals at a Westfield, Massachusetts, traprock quarry seem contemporaneous with green prehnite. Thin-bladed and often partially altered (to a bronze amphibole) crystals at Paterson and Great Notch, New Jersey, and in Poona, India, specimens.

Good crystals coat feldspar in pegmatites in granite at Baveno, Italy, and Arendal, Norway. Similarly in Devonshire, England. Actually too uncommon to justify inclusion here, but attractive and collectible with trophy satisfaction for collectors, especially those in Massachusetts.