Talc
Authors: Katie Ash, Diana Anderson, Charisma Baker
Mineral Name: Talc
Chemical Composition: Mg3Si4O10(OH)2
Color: Talc can be found in many colors but typically is green, grey, brown or clear (colorless).
Streak: Talc has a clear streak.
Hardness: Talc is a 1 on the Mohs hardness scale. It can easily be scratched or broken by fingernail. It has been known to be called the softest mineral on earth (1).
Cleavage/Fracture: Talc has one cleavage plane. It behaves like the mica minerals and peels into sheets, although sometimes this plane is hard to see because the softness of the mineral causes the planes to be distorted.
Crystal Form: Crystalline examples are almost always microscopic. (1) Most microscopic examples include the rare flat tabular crystals. (5) Talc can also be found in large masses and flakes or foliated sheets as well.
Luster: Talc has a luster that’s considered to be greasy, waxy, and/or pearly. (2)
Special Features: Talc has a 1 on the Mohs hardness scale, making it the softest of minerals. Its texture and feel is greasy to the touch. Talc is incapable of being dissolved.
Varieties: Talc does not have many varieties but one is soapstone, which is a massive variety if talc that can have impurities of chlorite and pyroxenes in it.
Mineral Group: Silicates are a group of minerals containing amounts of silicon and oxygen that are formed into a silica tetrahedra. The silicates represent the largest group of minerals. (1) Phyllosilicates are a mineral group that have each a set of tetrahedrons surrounded by three oxygen atoms.(1) Phyllosilicates are those that form sheets.
Environment: Talc is a metamorphic mineral and can be formed by at least two processes. (2) These two processes are contact metamorphism of carbonate rocks and hydrothermal alteration of magnesium-rich metamorphic and igneous rocks, like serpentinite and dunite, respectively. (3) In these processes the magnesium and silica found in carbonates or igneous rocks are dissolved in heated water and react with dolomitic marble. (2) These processes occurred in divergent plate boundaries of the Earth.
Associated Rock types: Associated rock types are Soapstone or Talc Schist. These are metamorphic rocks, and forms of talc and are high in magnesium. (9) All rocks that contain talc are metamorphic rocks.
Occurrence in North America: A Green form of crystallized talc can be found in the Vermont Verde Antique Quarry, and in Rochester, Vermont. Foliated green talc can be found in The Green Mountain Mine in North Carolina. And, last but not least, good quality talc can be found in Maryland and Montana as well as the serpentine belt on the state line of Pennsylvania.
Economic Uses: Talc is used to make soap and some makeup. (2) Talc is incapable of being dissolved in water making it useful for making talcum powder like that used on the insides of sterile gloves. Talc is used in ornamental sculptures due to its softness, making it easy to carve.
Industrial Uses: Talc can be used to make paper, plastics, paints, pharmaceuticals, and ceramics. (2) It has been used as an anti-stick coating agent in a number of popular foods including chewing gum, boiled sweets, cured meats, and for rice polishing. (5) A special form of talc can improve the performance of biological wastewater treatment plants.(5) Talc is beneficial for coating in painting as it improves the resistance to cracking and sagging. (5)
First Notable Identification: Georgius Agricola, a geologist in 1564, named talc, which is derived from the Arabic word “talq” meaning mica. It was a widely used ingredient in many ancient civilizations including Assyrians, Egyptians ( carving talc to make scarabs), and Native Americans. It is thought that the Egyptians used talc as a cosmetic ingredient. (4)
How We Identified It: It was identified by its low Mohs hardness of 1 and its greasy, soapy texture. Talc is very light color, from white to pink and at times will be greenish.
Don’t Confuse It With: Serpentine, Chlorite and Micas are some of the minerals that can be confused with talc. Serpentine has that greasy waxy feel to it, sometimes may even look like foliated green talc, and is easily mistaken for the mineral talc, although serpentine is definitely harder. Some Chlorites can be mistaken for talc due to the greasy/smooth look.(6) Chlorite is a form of green mica so it is closely related to talc and comes in various colors and sheets. Chlorite is referred to as an “unimportant green mineral that is found on the surface of other important minerals” so it is quite likely this mineral can be mistaken for the green talc. (7) However, again, chlorite is harder than talc.
Bibliography:
Friedman, Hershel. (2018). The Mineral Talc. Retrieved from Mineral.Net: http://www.minerals.net/mineral/talc.aspx
“Talc: The Softest Mineral.” Geology, http://www.geology.com/minerals/talc.shtml.
“The Softest Mineral in the World: Mineralogy and Geology www.mondominerals.com/en/talc-production/mineralogy-geology/
“Mineral Resource of the Month: Talc” www.earthmagazine.org/article/mineral-resource-month-talc
“What is Talc?”
http://www.ima-na.org/page/what_is_talc
(6) “Serpentine”
(7) “Chlorite”
http://www.minerals.net/mineral/chlorite.aspx?img=/image/1/182/chlorite.aspx
(8) “Talc carbonate”
http://rocks.comparenature.com/en/talc-carbonate-rock/model-88-0
(9) “Soapstone”
http://rocks.comparenature.com/en/talc-carbonate-rock/model-88-0