Sunday, March 23, 2008

A picture of a Borealis in a mineral: Labradorite

Picture: Dual view of a cleavage fragment of labradorite showing the multi-colored labradorescence (schiller effect) and the same area viewed without the color. The color is due to optical interference on the 010 polysynthetic twinning planes (Albite Law).

Next in my blog is tectosilicate "Labradorite" variety: Spectrolite ((Ca,Na)(Si,Al)4O8) in all probabilities named like that in honor of its color spectrum reflected in the tabular crystals as a gift for the eyes. Now, labradorite was named like that thanks to its original locality the Labrador Peninsula. Its beauty combined with its hardness have made the Spectrolite a beloved stone for kitchen tops, and floors.

I remember being in the Telephone company of Saudi Arabia to pay my bill while I lived there back in the 80's, and I was in owe watching such luxury, the whole building was labradorite variety spectrolite, I just couldn't believe it, and at least in those years, it was forbidden to take pictures.

Chemical Formula: (Ca,Na)(Si,Al)4O8
Molecular Weight = 271.81 gm
Empirical Formula: Na0.4Ca0.6Al1.6Si2.4O8
Environment: Magmatic and metamorphic rocks.
Locality: Labrador peninsula, Canada.
Name Origin: Named after its locality.
Synonym: Spectrolite
Crystal system: Triclinic - Pinacoidal
Cleavage: [001] Perfect, [010] Good, [110] Distinct
Color: Colorless, Gray, Gray white, White, Light green.
Density: 2.68 - 2.71, Average = 2.69
Diaphaniety: Translucent to transparent
Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern.
Habit: Crystalline - Coarse - Occurs as well-formed coarse sized crystals.
Habit: Granular - Generally occurs as anhedral to subhedral crystals in matrix.
Habit: Striated - Parallel lines on crystal surface or cleavage face.
Hardness: 7 - Quartz
Luminescence: Non-fluorescent.
Luster: Vitreous (Glassy)
Streak: White
Radioactivity: GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Labradorite is Not Radioactive

Have a great weekend, once again in Anaco Venezuela, but ready to back to Houston tomorrow morning from Caracas. In the meantime, feel free to visit my website:

Oscar el Mexicano

A picture of a Borealis in a mineral?: Labradorite var. Espectrolite

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