File:Celestite (South Bass Island, Lake Erie, Ohio, USA) 1 (40092150820).jpg

Celestite from Ohio, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are about 5400 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfate minerals all contain one or more sulfate anions (SO4-2).

Celestite (also known as "celestine") is a strontium sulfate mineral, SrSO4. Its name has the same etymology as "celestial", meaning "sky", in reference its bluish to pale bluish crystals. This mineral has a nonmetallic luster, a clearish to whitish to pale blue to bluish-gray color, a white streak, a 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.

The celestite crystal shown here was lining a cavity (vug) in Silurian carbonate rocks. The specimen is from a Lake Erie island in northern Ohio, which 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.) and Carlson (2015 - Minerals of Ohio, Second Edition, Ohio Geological Survey Bulletin 69 (Second Edition), 290 pp.).

From exhibit signage:

Crystals of celestite. These were collected on South Bass Island in 1901 and may well have come from what we know as Crystal Cave.

Ohio is famous for fossils but is not that well known for minerals, with a few exceptions. One of them is Crystal Cave on South Bass Island in Lake Erie. Most caves are lined with stalactites and stalagmites of the mineral calcit (calcium carbonate, CaCO3) but Crystal Cave is lined with large crystals of the mineral celestite (strontium sulfate, SrSO4), some of which were over a foot long.

Originally the celestite was mined for strontium, which was used to produce the bright red color of fireworks, but today you can go in the cave and see the crystals.

Locality: unrecorded/undisclosed site on South Bass Island, western Lake Erie, far-northern Ohio, USA

Photo gallery of celestite: