![Art Deco Green Chalcedony and Diamond Buckle Brooch. Art Deco Green Chalcedony and Diamond Buckle Brooch.](https://www.langantiques.com/university/wp-content/uploads/elementor/thumbs/art-deco-green-chalcedony-and-diamond-buckle-brooch_2_50-1-11044-q88k0gwqwnbimkdqzd7u5elnegyfn2zi2qdp3wucug.jpg)
Having crystals so small that individual crystals cannot be seen under an ordinary optical microscope, but are detectable by effect under crossed polars; a full rotation of a cryptocrystalline material between crossed polars will show the stone transmitting light in all positions. A good example of a cryptocrystalline material is chalcedony.