Chocolate dogtooth calcite, large

Chocolate dogtooth calcite, largeLocale: Santa Eulalia, Chihuahua, Mexico Approx size: 5. 5 x 3. 5 x 1. 75" Approx weight: 542g (a bit over 1 lb) 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 brown appearance from iron oxides; a layer of hematite included calcite is deposited on the surface during a

Locale: Santa Eulalia, Chihuahua, Mexico

Approx size: 5.5 x 3.5 x 1.75"

Approx weight: 542g (a bit over 1 lb)

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 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 yellow-brown interior. 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 shows signs of natural etching that have left the tip of many of the dogtooth crystals blunted or hollow. The cleaved crystals have concentric rings following the crystal structure, thin gaps dissolving from between.

Very small crystals often dot the surface of the calcite. A lot of the specimen is covered with a flaky thin off-white mineral overgrowth, which may by calcite. There are also tiny points of quartz tucked between crystals, some with a slight smoky-quartz tint. I suspect the very small botryoidal peach-colored crystal spotting the specimen (the largest is visible just right of center in image 4) may be the world's smallest rhodochrosite, also common from this locale.

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