Q: What is goldstone? Is it suitable for use in fine jewelry?
A: Goldstone is a glass with flecks of copper suspended in it. The glass is made in a reducing furnace with copper salts added, which “smelts” the copper salts back to copper, which then crystalizes. Its discovery was probably originally an accident, from adding too much copper-bearing mineral to the melt, and having a reducing atmosphere at the same time. (Normally, the copper minerals in an oxidizing furnace would have been used to create a number of colors in the glass.) The copper platelets suspended in the glass give it its characteristic glitter. Other coloring agents added to the glass can change the basic copper colored variety to a number of other versions, such as blue and green etc. But the glass only is colored. The sparkles are still the same copper crystals.
The stuff originated in Italy, and is still made there by members of a single monastic community. The story goes that it was for a long time a very closely guarded secret how they made it, and even now manufacture of the material remains the primary source of income for that monastery, though it’s also made elsewhere these days.
Because of this origin, all sorts of associations have been made with the stuff and the Christian church, and it’s thus commonly found in religious jewelry, and is used in strongly Catholic countries more than elsewhere. The Mexican jewelers use a good deal of the stuff, though my suspicion is that this is due to the fact that it’s cheap, and not the religious connotations.