Tobelite

Formula: (NH₄,K)Al₂(Si₃Al)O₁₀(OH)₂

Origin of name: after locality,  Ohgidani pottery stone deposit, Tobe, Ehime Prefecture, adn in the Horo pryophyllite deposit, Toyosaka, hiroshima Prefecture, Japan

Crystal system: Monoclinic

Crystal class: 2/m (probable)

Twinning:

Unit cell: a = 5.219, b = 8.986, c = 10.447, β = 101.31°

Colour: Yellowish green, pearly white

Diaphaneity: Transparent

Luster: Silky

Habit: Minute crystals and flakes to 0.1 mm, clay-like, massive, scaly

Hardness:  2

Specific gravity: 2.58-2.62

Cleavage: 1; {001} perfect

Tenacity: Clayey

Streak: White

Synonyms/varieties:

Comments:  Found as hydrothemal alteration of biotite andesite dike or in a hydrothermally altered rhyolite tuff.