If it’s very soft and feels a bit greasy and/or soapy, there’s a good chance it’s talc.

Physical Properties
Chemical formula Mg3Si4O10(OH)2
Class Phyllosilicate
Sheets of linked tetrahedra
Crystal system Monoclinic
Habit Usually massive
Usually very fine-grained
Rare tabular pseudohexagonal
Color Grey
Hardness 1
Specific gravity 2.8
Cleavage Perfect basal (001)
Fracture Flexible
Luster Resinous
Transparency Translucent
Streak White
Optical Properties
PPL Colorless
XPL 1st order greys and yellows
May appear smeared or
poorly defined
δ 0.05
Special properties
Soft, greasy feel
after Perkins, 320

Talc in Hand Sample


Talc in Thin Section

Thin Section GigaPans

Talc in plane polars

Talc in crossed polars

Talc, PPL
Talc, XPL

Further Reading

Talc at webmineral.com

Talc at mindat.org