Goldstone is one of the most attractive materials in the bead trade and one of the most misdescribed. It is glass — copper-coloured, brown or blue glass — in which metallic copper has been made to crystallise as thousands of tiny flat flakes that glitter in the light. It is entirely manufactured, has been since at least the seventeenth century, and is regularly sold as a natural "crystal", as "sunstone", or by the trade name "aventurine glass" with the word glass quietly dropped.
What goldstone is
Glass with dispersed metallic copper crystals. Properties: singly refractive (glass), RI about 1.5, SG about 2.5–2.8 (the copper adds weight), hardness about 5.5, and the diagnostic appearance: a dense, even distribution of bright, flat, angular copper flakes throughout a transparent brown (or, with cobalt, blue; or, with manganese, purple; or green) glass matrix. The flakes are all similar in size, all metallic, and give a uniform glitter from every angle.
What it is confused with
Aventurine quartz. A natural quartzite containing flakes of green fuchsite mica (green aventurine), or of hematite or goethite (reddish-brown aventurine). Properties: quartz — aggregate reaction on the polariscope, SG 2.65, hardness 7. The glitter (aventurescence) is from mica or oxide platelets, is less regular, less bright and less dense than goldstone's copper, and the body is translucent to opaque rather than glassy. Green aventurine is very common and genuine; brown goldstone is regularly sold as "brown aventurine" or "aventurine".
Sunstone (feldspar). A natural feldspar (oligoclase or labradorite) with aventurescence from hematite or copper platelets, giving a warm orange-red glitter. Properties: RI 1.53–1.55 (two readings), SG 2.62–2.67, hardness 6–6.5, doubly refractive, with the cleavage and twinning of feldspar visible under magnification. The glitter in Oregon sunstone is genuinely from copper, but the platelets are sparser, larger and more irregular than goldstone's, in a crystalline host. Goldstone is sold as "sunstone" constantly.
How the laboratory separates them
Polariscope. Goldstone stays dark or shows strain (glass). Aventurine quartz shows the aggregate reaction. Sunstone blinks (doubly refractive crystal).
Magnification. Goldstone: uniform, dense, angular copper flakes in a clear glass matrix, often with round gas bubbles. Aventurine quartz: irregular mica or oxide platelets in a granular quartz mass. Sunstone: sparse platelets in a crystal with cleavage planes.
SG and hardness support; RI on any flat surface confirms glass versus quartz versus feldspar.
Appearance. Goldstone is too regular. Nature does not distribute glitter that evenly.
Is it a fraud?
Goldstone sold as goldstone, or as aventurine glass, is an honest product with a long history. Sold as a natural crystal, as sunstone, or as aventurine (without "glass"), it is mis-described. A buyer who wants a natural stone, or who is paying a natural-stone price, deserves the word glass in the description.
Frequently asked questions
Is blue goldstone natural?
No. It is cobalt-blue glass with copper flakes, entirely manufactured, and often sold as "blue sandstone" or as a natural crystal.
What is the difference between goldstone and sunstone?
Goldstone is man-made glass. Sunstone is a natural feldspar. Both glitter; the resemblance ends there.
Is aventurine natural?
Aventurine quartz, yes — green, and less commonly blue, reddish-brown or orange, all from natural inclusions. "Aventurine glass" is goldstone.
Does goldstone contain real gold?
No. The flakes are copper. The name refers to the colour.
Is goldstone worth testing?
It is inexpensive, and a loupe usually settles it: dense, perfectly uniform metallic glitter in a glassy body is goldstone. Testing is worthwhile only where a piece was sold at a natural-stone price.