Cubic Calcedony

This is commonly called Cubic Hornstone, but is truly a Calceclony, as indeed are many things winch are commonly called Hornstone; and it is hard to show their distinguishing characters. This specimen came from Beer Alstone, where the curious Octaëdral Fluor is found on what is also called Hornstone—see tab. 26. The crystals are generally blunt edged, their solid angles truncated, and their surfaces minutely mammillated, which helps to distinguish them. This secondary crystallization almost exclusively belongs to this substance, although there are one or two instances of its being found in other substances, as in Steatite, but which is chiefly in the form of Quartz. All are scarce.

The name Hornstone I suppose to be taken from the resemblance the stone bears to horn; a great variety of stones have occasionally had that appellation given to them, which probably vary much in their ingredients, as some little mixture may help their appearance: thus we might possibly find Lime, Fluor, and Clay Horns tones.