Formula: (NH4)AlSi3O8 . 0.5H2O
Origin of name: For Arthur Francis Buddington (1890-1980), American geologist, Professor at Princeton University, Princeton, New Jersey, U.S.A.
Crystal system: Monoclinic
Crystal class: 2 or 2/m
Twinning: noted
Unit cell: a = 8.571 Å, b = 13.032 Å, c = 7.187 Å, b = 112.73°
Colour: Colourless
Diaphaneity: Transparent to translucent
Luster: Vitreous
Habit: Crystals microscopic, euhedral; anhedral to cryptocrystalline
Hardness: 5.5
Specific gravity: 2.32
Cleavage: 2; {001} good, {010} distinct
Tenacity: Brittle
Streak: Light gray, yellow when impure
Synonyms/varieties:
Comments: An anhydrous ammonium feldspar. Found as a low-temperature hydrothermal replacement of plagioclase in andesite altered by ammonia-bearing hot springs, in metasomatised rhyolitic ash-flow tuffs.
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