Vote for your favorite mineral in #MinCup26! - Sphalerite vs. Anorthite Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
First confirmed in-situ locality after the mineral was first described in 1802 from an old, loose crystal. Massive material was "from one-fourth to half an inch in diameter, of a grayish black colour, with the surface always more or less irised", "The crystals are very minute, being seldom greater in diameter than a common pin, and often much less; yet many are extremely perfect.", "They are often grouped, or or intersecting, and are very brittle. The form of the crystal is that of a compressed rectangular prism, usually truncated on the lateral edges, or a four-sided pyramid, two sides of which are, in most instances, unduly extended.", "Specific gravity 5.90" Torrey (1824). The gravity of four crystals tested by Shepard (1870) were 6.02, 6.03, 6.10, 6.19, making them columbite. Dana (1875) gives analyses showing about three times as much iron as manganese.
Habit:
massive, slender prisms
Colour:
black
Significance:
Classic locality for this mineral (see references.)
Chrysoberyl locality, Haddam, Middlesex County, Connecticut, USA