Aeschynite

Formula:  (Ce, Ca, Fe, Th)(Ti, Nb)2(O, OH)6

Origin of name:  from Greek for shame

 

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:

Unit cell:  a =  7.54 Å (data for Ce), b = 10.96 Å, c = 5.40 Å

 

Colour:  Black, brownish black, brown, brownsih yellow

Diaphaneity: Subtranslucent

Luster:  Adamantine, submetallic

Habit:  Crystals, prismatic acicular or tabular; massive

Hardness:  5 to 6

Specific gravity:  4.96 to 5.2

Cleavage:  2;{100} interrupted,  parallel (010) parting, when not metamict

Tenacity: Brittle

Streak:  Yellow, dark brown to black

 

Synonyms/varieties:  Blomstrandine, priorite, taiyite  - all refer just to [aeschynite-(Y)]

 

Comments:  Three distinct species with the extensions -Ce, -Nd, and -Y indicating the predominant rare earth cation in the formula. Dimorphous with lucasite-(Ce). Occurrence in nepheline syenites and alkali syenite massifs; in granite pegmatites; in carbonatites in alkalic rocks; as detrital mineral in placers.

 

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