24 Photos
Boracite
Chemical Formula	Mg3B7O13Cl
Species	Borates
Crystal System	Orthorhombic
Mohs Scale	7
Specific Gravity	2.95
Color	Blue green, colorless, gray, yellow, orange, brown, white, blue, pale green, dark green; colorless in transmitted light
Streak	White
Luster	Adamantine, Vitreous
Refractive Index	n = 1.658 - 1.662 n = 1.662 - 1.667 n = 1.668 - 1.673
Diaphaneity	Transparent, Translucent
Cleavage	None Observed
Fracture	Irregular/Uneven, Conchoidal
Crystal Habit：Crystalline, disseminated
Geological Setting：Bedded sedimentary deposits of gypsum and anhydrite; salt deposits; potash deposits of the oceanic type.

Boracite is a magnesium borate mineral with formula: Mg₃B₇O₁₃Cl. It occurs as blue green, colorless, gray, yellow to white crystals in the orthorhombic - pyramidal crystal system. Boracite also shows pseudo-isometric cubical and octahedral forms. These are thought to be the result of transition from an unstable high temperature isometric form on cooling. Penetration twins are not unusual. It occurs as well formed crystals and dispersed grains often embedded within gypsum and anhydrite crystals. It has a Mohs hardness of 7 to 7.5 and a specific gravity of 2.9. Refractive index values are nα = 1.658 - 1.662, nβ = 1.662 - 1.667 and nγ = 1.668 - 1.673. It has a conchoidal fracture and does not show cleavage. It is soluble in water.

Boracite is typically found in evaporite sequences associated with gypsum, anhydrite, halite, sylvite, carnallite, kainite and hilgardite. It was first described in 1789 for specimens from its type locality of Kalkberg hill, Lüneburg, Lower Saxony, Germany. The name is obviously derived from its boron content (19 to 20% boron by mass).