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Silky Blaucophane Crystals

The Mineral glaucophane

Glaucophane is named from a combination of the Greek words Glaukos, meaning "blue", and Phainelein, meaning "appearance", alluding to its bluish color. Glaucophane forms a series with the less-common Ferro-glaucophane, where Glaucophane is the magnesium-rich end member and Ferro-glaucophane is the iron-rich end member.
Chemical Formula Na2Mg3Al2Si8O22(OH)2
Composition Basic sodium magnesium aluminum silicate, often with some iron
Variable Formula Na2(Mg,Fe2+)3Al2Si8O22(OH)2
Color Blue, dark blue, and black with blue overtones
Streak Grayish blue
Hardness 5.5 - 6
Crystal System Monoclinic
Crystal Forms
and Aggregates
Crystals are usually prismatic with a diamond-shaped cross-section. Often in platy groups of small prismatic crystals. Also bladed, columnar, acicular, fibrous, and massive. Crystals are often striated lengthwise.
Transparency Translucent to opaque. Rarely transparent.
Specific Gravity 3.0 - 3.1
Luster Vitreous, pearly
Cleavage 1,2
Fracture Uneven, splintery
Tenacity Brittle
In Group Silicates; Inosilicates; Amphibole Group
Striking Features Blue color, crystal and cleavage habits
Environment In metamorphic schists and eclogites. Glaucophane is one of the components of blueschist rock, and is responsible for it bluish color.
Rock Type Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 2
Demand (1-3) 3

Glaucophane AUCTIONS

 -  Iron-rich variant of Glaucophane, which has iron dominating over the magnesium in a solid solution series. Ferro-Glaucophane is recognized by the IMA as a distinct mineral species with the following chemical formula: Na2Mg3Al2Si8O22(OH)2. There can be iron replacing some of the magnesium up to 50 percent.
 -  Transparent to translucent variety of blue Glaucophane.

Glaucophane is more common than often perceived, though collector specimens of this mineral are seldom encountered, hence the few localities listed here. Groups of prismatic blue crystals come from Groix Island, Brittany, France; and transparent blue crystals from Rio Oremo, Chiavolino, Biella Province, Italy. In the U.S., Glaucophane is a constituent of the blueschist rocks throughout the Coast Ranges of Northern California, Oregon, and Washington. Dark blue crystals have been found in Ward Creek, Cazadero, Sonoma Co., California.

Muscovite (Fuschite), Epidote, Actinolite, Jadeite, Almandine, Albite, Lawsonite, Omphacite, Rutile

Riebeckite - Usually darker in color.
Tourmaline - Harder, lacks good cleavage.

glaucophane PHOTOS
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