Talc

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 Gray
White
Hardness 1
Specific gravity 2.8
Cleavage Perfect basal (001)
Fracture Flexible
Luster Resinous
Silky
Transparency Translucent
Streak White
Optical Properties
PPL Colorless
Non-pleochroic
XPL 1st order grays and yellows
May appear smeared or
poorly defined
δ 0.05
Special properties
Soft, greasy feel
after Perkins, 320

Talc in Hand Sample

Talc

Talc in Thin Section

Thin Section GigaPans

Talc, plane polars
Talc, crossed polars
Talc tremolite schist, plane polars
Talc tremolite schist, crossed polars

Talc, PPL

Talc, Plane Polars

Talc in plane polarized light. Magnification: 100x Click here to watch this grain rotate in XPL: https://viewer.gigamacro.com/view/i9AFlqUzKxbbK0i4 Click her…

Talc, XPL

Talc, Crossed Polars

Talc in cross polarized light. Magnification: 100x Talc in plane polarized light. Magnification: 100x Click here to watch this grain rotate in XPL: https://v…

Talc tremolite schist, PPL

Tremolite, Plane Polars

Tremolite in plane polarized light. Magnification: 40x Rock: Talc-tremolite schist Click here to watch this grain rotate in XPL: https://youtu.be/jkghynKS-hQ…

Talc tremolite schist, crossed polars

Tremolite, Crossed Polars

Tremolite in plane polarized light. Magnification: 40x Rock: Talc-tremolite schist Click here to watch this grain rotate in PPL: https://youtu.be/w782ovG0SbA…

Further Reading

Talc at webmineral.com
Talc at mindat.org