Rectorite

Formula: (Na,Ca)Al₄(Si,Al)₈O₂₀(OH)₄.2H₂O

Origin of name: for E. Rector, American lawyer

Crystal system: Monoclinic

Crystal class: unknown

Twinning:

Unit cell: a = 5.13, b = 8.88, c = 23.85, β = 96.3°

Colour: White, yellowish to brownish white

Diaphaneity: Translucent (?)

Luster: Pearly to greasy when massive

Habit: Crystals, aggregates, earthy, matted masses resembling the "mountain leather" variety of palygorskite

Hardness: Less than 1

Specific gravity: 2.34 (calculated)

Cleavage: 1; {001} perfect

Tenacity: Flexible but not elastic, plastic and greasy when hydrated

Streak: White

Synonyms/varieties: Allevardite, Ca-rectorite, K-rectorite, Na-rectorite

Comments: A 1:1 regular interstratification of a dioctahedral mica and a dioctahedral smectite