• A large plate of dogtooth calcite with dark brown opaque coloration. The crystals are pointy, angled in different directions spreading out from the center. The luster is matte and rough.
  • Angled view of the specimen, a thin plate of calcite crystals, the top surface covered with well-formed spiky points. The edge is rough with several broken crystals.
  • Side-view of the specimen, a slightly curved plate of calcite. The broken edge shows a rough matrix base with a layer of broken yellow-brown calcite. The points on top are dark brown coated with an almost milky rough layer, with some points tipped in more tan translucent mineral.
  • Detail of the edge of the piece, the calcite showing etching patterns and several of the points with lighter tips. Just to the right of center in the image, there is a small round mineral on the edge of a calcite point that is a peachy pink color.
  • Side-view of the specimen, showing the piece has good even composition from multiple angles. Some of the faces on calcite points are smoother, others more rough.
  • Close detail view of the surface, showing rough texture on the points and between them from mineral deposition.
  • Close detail of the surface, focusing on a cleaved point that has left a flat, angled face. The face shows signs of etching into the surface, and color zoning of a lighter interior and dark brown border. Surrounding points have some translucency in the tips, their surfaces rough and whitish as if covered in ash. In areas, this lumpy overgrowth separates like scales.
  • Detail of the surface in an area where the overgrowth seems thick and translucent on the tips of points. Points are well-formed, with rough surface.
  • Side-view of the piece, showing layers of spikes across the length. There are a couple cleaved points in the foreground.
  • Side-view of the specimen, a somewhat thin curved plate of calcite with the crystals pointed to the left. The edge in the foreground has several cleaved crystals.
  • The backside of the piece, a rough rock matrix with a soft, dusty appearance.
  • Detail of a tiny quart point sticking out perpendicular from the side of a calcite point. Around it, some of the calcite points have slightly translucent tips. The white overgrowth appears like scales coating the calcite.
  • Scale image of the specimen on a measuring mat, measuring almost six inches long and three and a half inches wide.
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Chocolate dogtooth calcite, large

Chocolate dogtooth calcite, large

$28.00 USD
$28.00 USD
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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.

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