About Allophane

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  • Mineralogy and geology*

 

Mineralogy and Geology of Allophane

Mineral formula:  (Al2O3)(SiO2)1.3-2 · 2.5-3H2O

Crystal system: amorphous

Crystal habit: nano-balls of hydrous aluminumosilicate; a nano-mineral

Cleavage: none

Fracture: conchoidal

Color: white to shades of blue and blue-green, green, or brown

Streak: white

Luster: waxy

Diaphaneity: transparent to translucent

Moh’s scale hardness: 3

Streak: white

Specific gravity: 2.75

Named after:  the Greek άλλος ("allos") for "other" or "different" and φαίνεσθαι ("phaenesthai"), "to appear", in allusion to the change it undergoes in a blowpipe flame.

Geological occurrence: A weathering product of volcanic ash; in hydrothermally altered igneous rocks, from the breakdown of feldspars, and in hydrothermal veins, typically related to copper deposits. Also occurs in sedimentary rocks, including chalk and coal beds.

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* Mineralogical information is from mindat.org