Showcase Specimens 

 

 Ferroan Dolomite on Quartz

Dolomite - a

Dolomite - b Dolomite - c Dolomite - d Dolomite - e

CaMg(CO3)  - Calcium Magnesium Carbonate

 Dolomite has many uses. The most common is being used and an ornamental stone, or as a dietary supplement of calcium and magnesium. In it's massive form, dolomite is an important petroleum reservoir.

 

 

Selenite on Chalcedony

Selenite - a

Selenite - b Selenite - c Selenite - d Selenite - e

CaSO4 * 2H2O - Hydrous Calcium Sulfate

Selenite is a crystalline variety of Gypsum. Gypsum is an evaporite mineral used to make sheet rock. Selenite has no economic value, but it's highly prized to gem and mineral collectors, and as a secondary mineral in geodes.

 

 

Black Calcite on Quartz

 Black Calcite - a

Black Calcite - b Black Calcite - c Black Calcite - d Black Calcite - e

 (Ca,Fe)CO3 - Calcium Iron Carbonate

Stilpnosiderite is a film that forms on underlying calcite or quartz. Different colors of sheen are given to the calcite depending on the thinkness of the film. The black color is caused when the layers are too thick to reflect any other color of sheen.

 

 Perfect Calcite on Tan Calcite

Calcite - a

Calcite - b Calcite - c Calcite - d Calcite - e

CaCO3 - Calcium Carbonate

Calcite has many crystal habits and colors. It is mainly used as an ornamental stone and prized by mineral collectors.

 

Iridescent Brown Calcite

Aqua Sheen - a

 Aqua Sheen - b Aqua Sheen - c Aqua Sheen - d Aqua Sheen - e

 (Ca,Fe)CO3 - Calcium Iron Carbonate

Stilpnosiderite is a film that forms on underlying calcite or quartz. Different colors of sheen are given to the calcite depending on the thinkness of the film. The aqua color is caused when the layers are very thin.

 

 

Sphalerite on Quartz

Showcase - Sphalerite

Showcase - Sphalerite - a Showcase - Sphalerite - b Showcase - Sphalerite - c Showcase - Sphalerite - d

(Zn,Fe)S - Zinc Iron Sulfide

Sphalerite (also known as Blende), is an important ore of zinc. It can have excellent luster and be associated with many other minerals making it one of the best secondary minerals in Keokuk Geodes.

 

Pink Dogtooth Calcite

Showcase - Pink

Showcase - Pink - a Showcase - Pink - b Showcase - Pink - c Showcase - Pink - d

Calcite:CaCO3 with ingestion of Kaolinite:Al2Si2O5(OH)4 and topped with Pyrite:FeS2

The ingestion of the kaolinite alters the normal crystal structure of the calcite rhombohedral to scalenohedral (a.k.a dogtooth), and the color from clear/white to pink. This specimen is accented with dozens of perfect pyrite cubes.

 

Next Specimen : end of February

New specimens following monthly . . .