| Talc | |
|---|---|
 | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | Mg3Si4O10(OH)2 |
| IMA symbol | Tlc[1] |
| Strunz classification | 9.EC.05 |
| Crystal system | Monoclinic or triclinic[2] |
| Crystal class | Either prismatic (2m) or pinacoidal (1)[3] |
| Space group | C2/c or C1 |
| Unit cell | a = 5.291 Å, b = 9.173 Å c = 5.290 Å; α = 98.68° β = 119.90°, γ = 90.09°; Z = 2 or a = 5.287 Å, b = 9.158 Å c = 18.95 [Å], β = 99.3°; Z = 4[3] |
| Identification | |
| Color | Light to dark green, brown, white, grey, colorless |
| Crystal habit | Foliated to fibrous masses, rare as platey to pyramidal crystals |
| Cleavage | Perfect on {001} basal cleavage |
| Fracture | Flat surfaces (not cleavage), fracture in an uneven pattern |
| Tenacity | Sectile |
| Mohs scale hardness | 1 (defining mineral) |
| Luster | Waxy or pearly |
| Streak | White jot to pearl black |
| Diaphaneity | Translucent |
| Specific gravity | 2.58–2.83 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.538 – 1.550 nβ = 1.589 – 1.594 nγ = 1.589 – 1.600 |
| Birefringence | δ = 0.051 |
| Pleochroism | Weak in dark varieties |
| Ultraviolet fluorescence | Short UV: orange yellow; long UV: yellow |
| References | [3][4][5] |
Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant. It is an ingredient in ceramics, paints, and roofing material. It is a main ingredient in many cosmetics.[6] It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage and an uneven flat fracture, and it is foliated with a two-dimensional platy form.
The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 1 as the hardness of talc, the softest mineral. When scraped on a streak plate, talc produces a white streak, though this indicator is of little importance, because most silicate minerals produce a white streak. Talc is translucent to opaque, with colors ranging from whitish grey to green with a vitreous and pearly luster. Talc is not soluble in water, and is slightly soluble in dilute mineral acids.[7]
Soapstone is a metamorphic rock composed predominantly of talc.
- ^ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ W. A. Deer; R. A. Howie; J. Zussman, eds. (1992). An Introduction to the Rock-Forming Minerals (2nd ed.). Prentice Hall. ISBN 0-582-30094-0.
- ^ a b c Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1995). "Talc" (PDF). Handbook of Mineralogy. Vol. II (Silica, Silicates). Chantilly, Virginia: Mineralogical Society of America. ISBN 0962209716.
- ^ Talc, Mindat.org
- ^ Talc Mineral Data, WebMineral.com
- ^ "Talc". Minerals Education Coalition.
- ^ Profiles of Drug Substances, Excipients and Related Methodology, Volume 36 ISBN 978-0-123-87667-6 p. 283