Labradorite ((Ca, Na )(Al, Si )4O 8), a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It has an anorthite percentage (%An) of between 50 and 70. The specific gravity ranges from 2.68 to 2.72. The streak is white, like most silicates. The refractive index ranges from 1.559 to 1.573 and twinning is common. As with all plagioclase members, the crystal system is triclinic, and three directions of cleavage are present, two of which are nearly at right angles and are more obvious, being of good to perfect quality. (The third direction is poor.) It occurs as clear, white to gray, blocky to lath shaped grains in common mafic igneous rocks such as basalt and gabbro, as well as in anorthosites.
Viola labradorica, commonly known as alpine violet, American dog violet, dog violet, and Labrador violet, is a perennial. It is native to Greenland, eastern Canada, and the eastern United States. The plant sold as Viola labradorica by nurseries is Viola riviniana .