'Celestine' or 'celestite'
[1] (
SrSO4) is a
mineral consisting of
strontium sulfate. The mineral is named for its occasional delicate blue
color.

Celestine from the Machow Mine, Poland.
Celestine occurs as
crystals, and also in compact massive and fibrous forms. It is mostly found in
sedimentary rocks, often associated with the minerals
gypsum,
anhydrite, and
halite.
The mineral is found worldwide, usually in small quantities. Pale blue crystal specimens are found in
Madagascar.
The bodies of
Acantharea are made of celestine, unlike those of other
radiolarians which are made of
silica.
In carbonate marine sediments, burial dissolution is a recognised mechanism of celestine precipitation
[2]

Celestine geode section
The largest known celestine
geode is located near the village of
Put-in-Bay, Ohio on
South Bass Island in
Lake Erie. The geode is 35 feet in diameter at its widest point. It has been converted into a viewing cave, and the crystals which once composed the floor of the geode have been removed. The
Crystal Cave has celestine crystals as wide as 18 inches across and weighing up to an estimated 300 lb.
See also
★
List of minerals
References
1. Nickel, Ernie.; Nichols, Monte. Mineral Names, Redefinitions & Discreditations Passed by the CNMMN of the IMA, Materials Data, Inc., 2004, p. 26 - Celestine is the approved name for this mineral by the International Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN). Although ''celestite'' finds frequent usage in some minerological texts, the name has been discredited as a valid mineral name by this organization.
2. Baker, Paul A.; Bloomer, Sherman H. The origin of celestite in deep-sea carbonate sediments ''Geochimica et Cosmochimica Acta'', vol. 52, Issue 2, pp.335-339, 1988