Mohs hardness soft minerals

The mineral talc is extremely soft (Mohs hardness = 1), has good sHp, a density of 2.7 to 2.8 g/cm, and a refractive index of 1.58. It is relatively inert and nonreactive with conventional acids and bases. It is soluble in hydroduoric acid. Although it has a pH in water of 9.0 to 9.5, talc has Lewis acid sites on its surface and at elevated temperatures is a mild catalyst for oxidation, depolymerization, and cross-linking of polymers. 

Substances, mostly minerals, are ranked by their ability to scratch one another. If one mineral can scratch another mineral it gets a higher ranking on the Mohs hardness scale. When Friedrich Mohs devised the scale, diamond was the hardness substance known, so it was given a value of 10. Talc (also known as talcum powder), being very soft, has a hardest rating of only 1. Mohs devised this scale to help sort out the private rock collection of an Austrian banker, and later the Archduke s museum collection. There are more quantitatively accurate measurements of hardness available today, but the simplicity of the Mohs scale keeps it relevant and practical. 

Mohs hardness. Based on an empirical scale for determining the relative hardness of mineral or mineral-like materials. The scale is based on the ability of one crystal to scratch another and ranges from a value of 1 (talc, soft) to 10 (diamond, hard), molality (molal concentration). A concentration in which the amount of solute is stated in moles and the amount of solvent in kilograms, molarity. The concentration of a solution in moles per liter. 

Also known as soapstone, talc has been used for thousands of years. It is characterized by its soft greasy feel. It is the softest of the minerals, with a Mohs hardness of 1-1.5. This softness also makes it easy to carve and shape. Exquisite ornamental serving utensils made of carved talc have been found dating back to antiquity. 

Calcium carbonate exists in three crystal modifications, aragonite, calcite and vaterite, but only the calcite form is of real importance. Because of calcite s perfect rhombohedral cleavage, it is a soft mineral with a Mohs hardness of 3.0. It has a specific gravity of 2.7 and is birefringent having refractive indices of 1.65 and 1.48. 

Magnesium hydroxide is a white crystalline material. Its specific gravity is 2.4. Like ATH, it is soft and non-abrasive with a Mohs hardness about 3. It starts to decompose at about 300 °C. The naturally occurring mineral is known as brucite. The natural crystal form is as a flat hexagonal shaped plate. 

TALC. 3Mg0-4Si02-H20. Talc is a hydrous magnesium silicate, with the composition 63.4% SiOj, 31.9% MgO and 4.7% HjO when found in pure form. It is an extremely soft mineral with a Mohs hardness of 1, has a platy structure and it is naturally hydro-phobic. Talc occurs as a relatively pure massive mineral in Montana, Australia and China. Elsewhere it occurs in conjunction with magnesite (Vermont, Quebec, Ontario and Finland), with tremoUte and serpentine in New York and with chlorite in France and Austria. In many ceramic applications, the presence of non-talc minerals such as chlorite and tremolite are beneficial. 

Talc (Washabaugh, 1988 Radosta, 1978) - Talc is a naturally occurring magnesium silicate mineral. The material is very soft (Mohs hardness of one) and most talcs are white with a bluish undertone. Talc is commercially... 

Soft crystalline solid rhombic crystal pure salt is white but color may vary the color of the mineral barite may vary among red, yellow, gray or green depending on impurities density 4.50 g/cm refractive index 1.64 melts around 1,580°C decomposes above 1,600°C hardness 4.3 to 4.6 Mohs insoluble in water (285 mg/L at 30°C) and alcohol Ksp 1.1 x 10-i° soluble in concentrated sulfuric acid. 

Soft, white metal with bluish tinge. Emits a tin Cry on bending. Ductile, malleable, softer than lead, leaves a mark on paper. Quite stable in air. Crystallizes and is diamagnetic, d 7.3. mp 155. bp 2000". Sp heat 0.0568 cal/g/ C. Hardness (Mohs ) = 1.2. Unaffected by water attacked by mineral acids. Very resistant to alkalies. 

Mica minerals are quite soft and nonabrasive so equipment wear is minimal. The hardness of mica minerals on the mohs scale of hardness varies from 2.0 to 2.5 mohs for muscovite mica and 2.5 to 3.0 mohs for phlogopite mica. 

Another mechanical property that may be important to consider is hardness, which is a measure of a material s resistance to localized plastic deformation (e.g., a small dent or a scratch). Early hardness tests were based on natmal minerals with a scale constructed solely on the ability of one material to scratch another that was softer. A qualitative and somewhat arbitrary hardness indexing scheme was devised, termed the Mohs scale, which ranged from 1 on the soft end for talc to 10 for diamond. Quantitative hardness techniques have been developed over the years in which a small indenter is forced into the surface of a material to be tested under controlled conditions of load and rate of application. The depth or size of the resulting indentation is measured and related to a hardness number the softer the material, the larger and deeper the indentation, and the lower the hardness index number. Measured hardnesses are only relative (rather than absolute), and care should be exercised when comparing values determined by different techniques. 

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