Is a Calcium Sodium Aluminum Silicate with formula Ca(50-70%) Na(50-30%) (Al, Si)AlSi2 O8 and hardness 6-6.5
Is a fascinating mineral that belong to the plagioclase series. The plagioclase series comprises feldspar that range in chemical composition from pure NaAlSi3 O8 to pure CaAl2 Si2 O8 . Labradorite is defined at approximately the 50% to 70% CaAl2 Si2 O8 . Labradorite by definition must contain 50-70% calcium to 50-30% sodium in the sodium/calcium position of the crystal structure. All members of the plagioclase series usually display lamellar twinning called "Albite Twinning". The twinning is caused by a error in the crystal structure during its growth. It’s name comes from the labradorescenze effect: a truly amazing fenomenon due to different speed of the light passing through the parallel crystal layers. This effect is visible only on a certain light direction and during the cutting is essential the orientation of the stone. Polished on top only.