Ontario Mineral - Epidote

 

Rocks minerals Ontario Epidote

Chemistry:

 Ca2(Al, Fe)3(SiO4)3(OH), Calcium Aluminum Iron Silicate Hydroxide.

Class:

 Silicates

Subclass:

 Sorosilicates

Group:

 Epidote

Uses:

 mineral specimens and rarely as a gemstone.

Color:

 "pistachio" green to yellowish or brownish green, also brown to black.

Luster:

 vitreous

Transparency:

 crystals are transparent to translucent.

Crystal System:

 monoclinic; 2/m

Crystal Habits:

 include long, somewhat prismatic or tabular crystals with a typically dominant pinacoid that the crystal is often flattened against. The terminations are wedge shaped or tappered pyramids. Many clusters show grooved slender crystals or acicular sprays. Also massive, fiberous or granular.

Cleavage:

good in one direction lengthwise

Fracture:

 uneven to conchoidal.

Hardness:

 6-7

Specific Gravity:

 3.3-3.5

Streak

 white to gray

Other Characteristics:

 striated to the depth of grooves in some crystals.

Associated Minerals:

 calcite, biotite, hornblende, actinolite, andradite garnet and other metamorphic minerals

Local Occurance:

 Bessemer Mine

Best Field Indicators:

 only one direction of cleavage, crystal habit, color and hardness.

Description:

Epidote is a structurally complex mineral having both single silicate tetrahedrons, SiO4, and double silicate tetrahedrons, Si2O7. The formula of epidote could be expressed in a such a way so as to reflect this organization; Ca2(Al, Fe)Al2O(SiO4)(Si2O7)(OH). The two aluminums represent the parallel chains of AlO6 and AlO4(OH)2 octahedra that are the heart of the epidote structure. The silicate groups and extra ions connect the chains together. Since the chains are parallel, the crystals tend to be prismatic. The chains are arranged in parallel planes and the perfect cleavage breaks the bonds between these planes. Epidote, while not general known for exceptional crystals can produce some magnificent specimens. Its unique green color which is often described as "pistachio", is quite striking in well colored specimens.