Datolite

Datolite is a calcium boron hydroxide nesosilicate, CaBSiO4(OH). Datolite crystallizes in the monoclinic system forming prismatic crystals and nodular masses. The luster is vitreous and may be brown, yellow, light green or colorless. The Mohs hardness is 5.5 and the specific gravity is 2.8 - 3.0. The type localities are in the diabases of the Connecticut River valley and Arendal, Aust-Agder, Norway. Associated minerals include prehnite, danburite, babingtonite, epidote, native copper, calcite, quartz and zeolites. It is common in the copper deposits of the Lake Superior region of Michigan. It occurs as a secondary mineral in mafic igneous rocks often filling vesicles along with zeolites in basalt. Unlike most localities throughout the world, the occurrence of datolite in the Lake Superior region is usually fine grained in texture and possesses colored banding. Much of the coloration is due to the inclusion of copper or associated minerals in progressive stages of hydrothermal precipitation.
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(n.)
A borosilicate of lime commonly occuring in glassy,, greenish crystals.
  

General Information:
 Chemical Formula:
CaBSiO4(OH)
 Composition:
(Molecular Weight = 159.98 gm)
Calcium 25.05 % Ca
Silicon 17.56 % Si
Boron 6.76 % B 
Hydrogen 0.63 % H 
Oxygen 50.00 % O 
 Empirical Formula:
CaB(SiO4)(OH)
 Environment:
Secondary mineral in basic igneous rocks.
 Locality:
Diabases of the Connecticut River valley, USA.
 Name Origin:
From the Greek, dateisthai, meaning "to divide," because granular aggregates crumble readily.
Physical Properties:
 Cleavage:
None
 Color:
brown, colorless, yellow, white, or light green.
 Density:
2.8 - 3, Average = 2.9
 Diaphaniety:
Transparent to translucent
 Habits:
Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Granular - Generally occurs as anhedral to subhedral crystals in matrix., Porcelainous - Fine-grained, translucent massive material like broken china
 Hardness:
5.5 - Knife Blade
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
white
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