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The chemical formula of the mineral talc is Mg3Si4O10(OH)2. It is a composition of magnesium, silicon, hydrogen, and oxygen often referred to as a hydrated magnesium sheet silicate. The molecular drawing of talc below shows how it occurs as foliated masses. The layered formation of talc sheets are also referred to as platelets (minute flattened bodies). The middle layer is composed of magnesium-oxygen/hydroxyl octahedra (eight plane faces) and the two outer layers are composed of silicon-oxygen tetrahedra (four plane faces). Each platelet is held together by the Van der Waal's bond which makes it very easy for platelets to slide apart. This is why talc has perfect cleavage in one direction and explains its soapy soft texture when touched.

Talc generally occurs in two morphologies. An individual talc platelet can vary in size from approximately 1 micron to over 100 microns. Talc composed of large individual platelets is considered macro-crystalline (image bottom left), while talc that is composed of compact individual platelets is considered microcrystalline (image bottom right).


Talc is commonly referred to as the softest mineral known, however it has several other properties that include: Platyness (flaky layers), Hydrophobicity (lacking affinity for water / can have a carrier or barrier effect), Organophyly (attraction of non-polar substances, like organic minerals, to each other), Inertness, and Non- Polarity. These properties are responsible for talc’s special qualities of anti-caking, non-abrasiveness, printability, and adsorbability. Plus it has a low thermal expansion and can be used for elctro-insulating. Talc is resistant to water, weak acids, and alkalis. It is neither flammable nor explosive, but will start to lose its hydroxyl groups when heated to 900ºC. If talc reaches extreme temperatures of 1050ºC, it will re-crystallize into a different form called enstatite (anhydrous magnesium silicate, Mg2Si2O6)....