Celestite (a.k.a. celestine) is a strontium sulfate mineral, SrSO4. Its name has the same etymology as "celestial", meaning "sky", in reference its pale bluish crystals. This mineral has a nonmetallic luster, clearish to whitish to pale blue to bluish-gray color, white streak, hardness of 3 to 3.5, two cleavages, and is noticeably heavy for its size. It forms diagenetically and also occurs in low-temperature hydrothermal vein systems.
Celestite (field of view 4.5 cm across) from a quarry at the small town of Clay Center in Allen Township, Ottawa County, northwestern Ohio, USA. Here, celestite occurs in dolostone cavities (vugs) of the Lockport Dolomite (upper Niagaran Series/Wenlockian Series, Middle Silurian). This locality is on the southeastern flanks of the Michigan Basin. The strontium-rich fluids from which the celestite crystallized apparently traveled updip from the Michigan Basin. For more info. on Ohio celestite, see Carlson (1991, Minerals of Ohio, Ohio Geological Survey Bulletin 69, 155 pp.).
Celestite (field of view ~3.8 cm across) from a quarry at Clay Center in Allen Township, Ottawa County, northwestern Ohio, USA (same locality & geology as 1st specimen shown above).
Celestite from the Newport Quarry (a.k.a. Holloway Quarry), Monroe County, Michigan, USA. Specimen owned by Bob Nowakowski.
(same general geology as above specimens).