Prehnite Epidote Mineral Specimen for you. Nice pale green Prehnite ball on the side of Chisel terminated Epidote. Dark green almost black Epidote, this specimen is from old stock. The Prehnite ball is about 1.8cmD.
6cm x 6.2cm x 4cm, 134g.
Prehnite: Ca2 Al2 Si3 O10(OH)2
Calcium Aluminum Silicate Hydroxide.
Prehnite is often found with zeolites and is sometimes thought of as a zeolite. But zeolites are actually Tectosilicates and Prehnite is a member the Phyllosilicates Subclass. Like zeolites, Prehnite can give off water when heated, but can not gain the water back like they can.
Its colour is a pleasant green and is at times quite unique to Prehnite. Some Minerals that can be confused with Prehnite include Gyrolite, Smithsonite and Hemimorphite. Prehnite is harder than all of these and lacks Smithsonite’s unusual luster. Hemimorphite is usually blue and Gyrolite is not as glassy.
Calcium Aluminum Iron Silicate Hydroxide
Epidote Crystal Habits include long, prismatic or tabular crystals. The terminations are wedge shaped or tapered pyramids. Many clusters show grooved slender crystals or acicular sprays. Also massive, fiberous or granular.
Epidote is a structurally complex mineral having both single silicate tetrahedrons, SiO4, and double silicate tetrahedrons, Si2O7. 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. Epidote, while not general known for exceptional crystals can produce some magnificent specimens.
Color is “pistachio” green to yellowish or brownish green, also brown to black.
Luster is vitreous.
Transparency crystals are transparent to translucent.
Crystal System monoclinic; 2/m
Crystal Habits include long, prismatic or tabular crystals with a typically dominant pinacoid that the crystal is often flattened against. The terminations are wedge shaped or tapered pyramids. Many clusters show grooved slender crystals or acicular sprays. Also massive, fiberous or granular.
Cleavage good in one direction lengthwise.
Fracture is uneven to conchoidal.
Hardness is 6-7
Specific Gravity is 3.3-3.5
Streak white to gray
Associated Minerals calcite, biotite, hornblende, actinolite, andradite garnet and other metamorphic minerals.
Other Characteristics: striated to the depth of grooves in some crystals.
Notable Occurances Untersulzbachtal, Austria; Italy; Baja, Mexico and many localities in the USA.
Best Field Indicators only one direction of cleavage, crystal habit, color and hardness.