Minerva # 1 Mine, Cave-in-Rock, Hardin County, Illinois

BaCaCo₃

The pale yellow Fluorite on this specimen has quite an unusual shape. There seems to be some controversy over how specimens with similar shapes were formed. There is a theory that these shapes are caused by acid etching. However, Fluorite is fairly resistant to acids and under the Calcite coating there is unetched blue Fluorite. More likely, this Fluorite formed around the voids between spherical Barite which was later etched away by a solution containing Hydrofluoric acid (to which Fluorite is resistant). Be that as it may, the result is some of the most unusual shaped Fluorite to be found anywhere. Much later, a layer of carbonates formed on the underlying Blue Fluorite (but not on the yellow Fluorite?). This consists of Calcite crystals which are covered with a secondary coating. This coating could be Alstonite, Strontianite or Benstonite, all of which occur in this mine in similar associations. Also, there is one very nice hexagonal Withereite crystal. This Witherite crystal fluoresces a bright blue/white under LW UV, the overcoating on the Calcite a pale cream color and the yellow Fluorite is a pale pinkish purple.

From the Reed Meyers collection

6.5 x 4.8 x 5.3 cm

Sold Specimen retained as part of the Minerals Sold But Not Forgotten Galleries