twinned Calcite

The Jeffersonville Limestone (lower Middle Devonian) occupies an area south and west of the Kankakee and Cincinnati arches that is about half the size of Indiana, it's known for the tremendous coverage, the production of fossils, and spectacular calcite.

Pendelton Quarry (Irving Materials Quarry) produced some of the most well-known twined calcites in the States. These calcite are usually found in vugs on the limestone wall, probable indicates a post-forming mineralization that when carbonate-bearing fluid through the empty spaces. I don‘t know what mechanism made the macroscopic twins, but microscopic twins sometimes can be used to estimate palaeostress or thermal deformation as a thermometer.

Unfortunately, not many pieces were preserved. Doesn't like shale, limestone is a hard chemical sedimentary rock that's hard to mine crystals without damaging. The piece featured here is one of the few floaters that I have seen, and I am glad for having a big one.

3.2cm, Irving Materials quarry, Anderson, Madison County, Indiana. Ex Rock Currier, Jingnan (Tom) Zhang Coll, Jeff Scovil photo.