The origin of the large deposits of Celestine that abound in certain beds of Triassic age has long been a puzzle to Geologists. At Bristol, Celestine is found only on the lowest beds of the Keuper marls resting on the solid red sandstone rock, and may be collected by the ton.

It occurs in large masses, in veins and in geodes, accompanied by Selenite. In many of the concretions the crystals are long and acicular, radiating from the centre. In other places they seem to be a simple aggregation of crystals so loosely bound together that they may be easily rubbed asunder by the slightest pressure of the fingers. The most beautiful forms, however, are those in the interior of the geodes. They are very large tabular prisms with the angles, edges and planes clearly defined. Their colour is white with a delicate bluish tint, and tolerably transparent, having a diameter frequently as much as an inch.