Goldstone is a glass with flecks of copper suspended in it. The glass is made in a reducing furnace with copper salts added; the copper platelets suspended in the glass give it its characteristic glitter. Goldstone has been around since the European Renaissance.
Stories say that it was discovered by Venetian monks when by accident, molten copper tipped into a molten glass container. This crystallized into thousands of tiny crystals and formed a melt with golden light sparkles.
Made in Italy and China.
Mohs hardness 5.5.