This a Grade 'A' Labradorite Cab is approximately 20.5 x 25 mm; thickness is 6.5 mm, with a weight of approximately 4.44 grams. The back of this cab is flat. 
 
Labradorite is a feldspar with flashes known as Labradorescence. Most common colors are blue, green and gold. Rare colors are reds, pinks and purples. Alternate name is Spectrolite. It has a hardness of 6-6.5 Mohs and can be found in Madagascar, New York, Finland, China and Canada.