Stepped Calcite, Rensselaer Quarry, Rennselaer, Indiana
This is a rare and unique fluorescent calcite specimen from the Rensselaer Quarry, Pleasant Ridge, Jasper County, Indiana that shows a very unusual stepped crystal habit. This piece features a large grouping of intergrown, translucent, golden-honey colored, highly modified, stepped rhombohedral calcite crystals. As is typical for the Rensselaer location, this specimen is coated with dark bitumen. This specimen is at its best under mid wave UV, with the bitumen showing yellow-tan fluorescence which contrasts nicely against the pink response of the underlying calcite. This specimen measures 85 x 84 x 74 mm and it weighs 510 grams.
The Rensselaer Quarry, also known as the Pleasant Ridge Quarry, is located approximately 3 miles east of Rensselaer, Indiana. The quarry is a former open pit producer of dolostone aggregate, but is now closed and flooded with water. Natural bitumen commonly permeates the dolostone and often coats the mineral specimens collected there.
The photograph above shows fluorescence under mid wave UV (302 nm). The bitumen coating shows a yellow-tan response while the underlying calcite fluoresces pink. Note that the pink fluorescence of the underlying calcite is only visible in areas of the specimen where the bitumen coating is thin, or has rubbed off. The bitumen shows a similar fluorescent response under all UV wavelengths, but the calcite is only weakly fluorescent under short wave (254 nm) and long wave (365 nm) UV.
The same specimen shown under visible light. Note the dark brown to black bitumen staining and coating. The crystals also contain bitumen inclusions.