Dolomite – an often under-appreciated mineral

Dolomite is another common mineral in sedimentary rock. It’s a carbonate mineral CaMg(CO₃)₂. Crystals are usually rhombic though growth can create a saddle-shape crystal. Color is commonly pearly white, but it can be pink, yellow, orange, brown or red. Those with the reddish tinge have iron in the atomic structure and are called ferroan dolomite.

Corydon Crushed Stone Quarry in Harrison Co., Indiana, is a top 3 or 4 American locality for its pink color. Intensity is variable and the color disappears if the specimen is left outside for a period of months or years.

This specimen I won as a door prize at my very first Kyana Geological society meeting I attended as a "Pebble Pup" in 1969. — This specimen I won as a door prize at my very first Kyana Geological society meeting I attended as a “Pebble Pup” in 1969.

This pink dolomite has small calcite crystals that formed later.

A close-up of dolomite is saddle-shaped crystals, colored by iron and sprinkled with manganese oxide blebs.

Intense pink dolomite from the upper vuggy zone (often has bigger crystals)

Dolomite encrusting calcite; from the upper vuggy zone. — Dolomite encrusting calcite; from the upper vuggy zone

Harrodsburg, Monroe Co., Indiana, is a famous collecting locality for geodes. One of my favorites is the dolomite with a little iron giving it a vivid color.

Ferroan and regular dolomite on quartz in a geode

Sellersburg Quarry, Clark Co., Indiana, has rare vugs of dolomite, calcite and pyrite in the Jeffersonville Limestone.

Dolomite in pale, pearly curved crystals. This is the best specimen Alan collected.

Lebanon Quarry, Marion Co., Kentucky, has pale dolomite crystals in a dolostone breccia and in rare calcareous nodules in the New Albany Shale.

Light pink-brown dolomite with needle-like crystals of goethite in a New Albany Shale calcareous nodule.. — Light pink-brown dolomite with needle-like crystals of goethite in a New Albany Shale calcareous nodule.