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