Mineral description : Labradorite

Labradorite from Ylämaa, Finland.

Mineral class	Silicates : Tektosilicates : Feldspar group
Chemical formula	(Ca,Na)(Si,Al)4O8 (50-30% Na, 50-70% Ca)
Crystal system	Triclinic.
Habitus	Tabular to prismatic crystals. Commonly with polysynthetic twinning. The twinning is very easy to see in labradorite. Often as granular or compact masses.
Cleavage	Perfect in one direction, good in another with 90 degrees angle. Fracture uneven to conchoidal.
Hardness	6-6.5
Density	2.70
Color	White, bluish to dark gray. In some directions it shows a rich play of colors
Streak	White
Luster	Vitreous to pearly. Transparent to translucent.
Description	Often quarried for jewelry and monumental stone.
Occurance	A major part in rocks as diabas basalt and gabbro, more rarely in granitic rocks.
Associates
Notes	Look for the color play on broken surfaces. Soluble in acid when powdered.
Locations	A common mineral. Tabergsgruvan, Småland. As cm sized grains in magnetite-olivine. Fredriksnäs, Valdemarsvik, Östergötland. As grains in gabbro. North-east of Nordingrå, Ångermanland. As anortosite. Ylämaa, Finland. As the gemmy variety spectrolite. Up to dm sized crystals in anortosite. Upper part of the Sogne fjord, Norway. As complete mountains of anortosite. Larvik, Norway. As rock called larvikite.

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