Chocolate dogtooth calcite, large

Locale: Santa Eulalia, Chihuahua, Mexico

Approx size: 5 x 3 x 1.75"

Approx weight: 372g

Known by the trade name "chocolate dogtooth calcite," this type of calcite from the famed Santa Eulalia mining district grows in hedgehog clusters of sharp dogtooth (scalenohedral) crystals. The variety gets its distinctive opaque dark brown appearance from iron oxides; a layer of hematite-included calcite is deposited on the surface during a later phase of growth.

Broken crystals reveal the first phase of growth had some translucency with dark brown borders. Calcite has perfect cleavage so it is common to have a point or two that has cleaved off, leaving a flat smooth window displaying this growth. This specimen has a nice cluster of three cleaved points near the center.

Very small crystals often dot the surface of the calcite. There is a flaky thin white mineral overgrowth on some of the points which may be calcite. Several tiny points of quartz are also tucked between crystals, some with smoky-quartz coloration.

UV reactivity: the presence of iron dampens any reaction in the brown calcite, which is non-reactive. This piece has limited reaction.