Gypsum hardness

A mineral s hardness is defined as its ability to scratch another mineral. This is usually measured using a comparative scale devised about 200 years ago by Friedrich Mohs. The Mohs scale lists ten common minerals, assigning to each a hardness from 1 (talc) to 10 (diamond). A mineral can scratch all those minerals having a lower Mohs hardness number. For example, calcite (hardness three) can scratch gypsum (hardness two) and talc (hardness one), but it cannot scratch fluorite (hardness four). 

Fracturing of Model Minerals. Further insight into the processes responsible for liquid SO2 fracturing of these shales is provided by the behavior of several minerals when subjected to liquid SO2. Authenic samples of calcite (crystals), dolomite (hard lumps), gypsum (hard lumps), and illite (hard lumps) were treated with liquid SO2 at 25°C for 2-5 hours after removal of the SO2, the treated minerals were heated for 2 hours at 100°C infrared spectra and sulfur analyses were then obtained. Calcite crystals developed numerous fine cracks and a fine powder flaked off. Although the powder contained no sulfur (elemental analysis) or S-0 moieties (IR spectra), the cracked crystals were shown to contain 0.18% sulfur in the form of sulfur-oxygen structures. Although these data are consisted with a 0.7% conversion via... 

The siHcone impression materials are very compatible with gypsum products, give casts having exceUent hard surfaces, and can be electroplated with either copper or silver. However, the acidic copper sulfate bath gives more acceptable results. 

The hardness of a mineral as measured by the Mohs scale is a criterion of its resistance to crushing [Fahrenwald, Trans. Am. In.st. Min. Metall. Pet. Eng., 112, 88 (1934)]. It is a fairly good indication of the abrasive character of the mineral, a factor that determines the wear on the grinding media. Arranged in increasing order or hardness, the Mohs scale is as fohows 1, talc 2, gypsum 3, calcite 4, fluoride 5, apatite 6, feldspar 7, quartz 8, topaz 9, corundum and 10, diamond. 

Calcium sulfate hemihydrate []0034-76-1 j M 145.2. Sol in H2O (0.2 parts/100 at 18.75°). Completely dehydrated >650°. Dry below 300° to give a solid with estimated pore size ca 38% of vol. Anhydrous CaS04 has high affinity for H2O and will absorb 6.6% of its weight of H2O to form the hemihydrate (gypsum). It sets to a hard mass with H2O, hence should be kept in a tightly sealed container. 

X-ray evidence shows the material to be completely amorphous as might be expected from such a complex mixture. The specific gravity ranges from 1.05 to 1.10. It is slightly harder than gypsum and therefore just not possible to scratch with a fingernail. Yellow in colour, it is less brittle than other hard natural resins and may therefore be carved or machined with little difficulty. The refractive index is 1.54. 

The hardness test sometimes is performed on the mud as well as the mud filtrate. The mud hardness indicates the amount of calcium suspended in the mud as well as the calcium in solution. This test usually is made on gypsum-treated muds to indicate the amount of excess CaSO present in suspension. To perform the hardness test on mud, a small sample of mud is first diluted to 50 times its original volume with distilled water so that any undissolved calcium or magnesium compounds can go into solution. The mixture then is filtered through hardened filter paper to obtain a clear filtrate. The total hardness of this filtrate then is obtained using the same procedure used for the filtrate from the low-temperature low-pressure API filter press apparatus. 

The amount of hardness present in natural surface and groundwaters depends to a large extent on the action of dissolved carbon dioxide in rainwater on the watershed s geological formations (such as limestone, dolomite, gypsum, or magnesite). The dissolved hardness levels remain relatively low because of the sparingly soluble nature of the salts formed. Typically, MU water sources initially contain anywhere from 5... 

Soft and friable Sulphur, gypsum Cone crushers Ball, pebble and Ball, pebble and Moh s hardness... 

Silver white, relatively soft metal that is only applied in alloys. Oxygen and water attack pure Ca. The most prominent compound is the oxide (CaO) = burnt calcium, which hardens to calcium carbonate in mortar. Annual production of about 120 million tons. Burnt gypsum (CaS04 0.5 H20) hardens with water. A great step in evolution was the replacement of hard shells of brittle calcium carbonate by an internal skeleton of tough calcium phosphate (hydroxylapatite)-protein composite. Calcium is essential for all life forms. The daily requirement is 0.7-1.0 g. Humans (70 kg) contain 1 kg of calcium. Calcium silicate is the main component of cement. Marble is calcium carbonate in polycrystalline form and the favorite material of sculptors. 

Plaster of Paris has long been used as a casting material, a cement, and a mortar. If mixed with water, plaster of Paris forms a very soft and pliable mixture. After a very short time, lasting only 5-8 minutes, the wet, pliable mixture sets, that is, it hardens into a stable, firm solid. The setting process entails the incorporation of water molecules (a process known as hydration) into the calcium sulfate hemihydrate and the consequent formation and crystallization of hydrated sulfate of calcium. In other words, when water is added to plaster of Paris, the two combine, again forming gypsum, which soon crystallizes into a hard solid mass ... 

Gypsum, 4 582-601 5 467, 785t 23 576 forms and composition, 4 583t hardness in various scales, 7 3t in Portland cement, 5 467 in Portland cement hydration, 5 477t thermal reduction of, 23 577 thermodynamics and kinetics of formation- decomposition, 4 586-588 Gypsum board, 4 600-601 Gypsum processes, obtaining sulfur from, 23 576-577... 

Used in mining metallic ores, gypsum, limestone, in quarrying hard rock, and in construction work (Refs 1 2). Compositions are not given, but their bulk strengths, densities and detonation velocities are Listed in Ref 3 Refs 1) Cook (1958), 12 2) CondChem-... 

Gypsum (Calcium Sulfate Dihydrate, Alabaster), CaSO4.2H20 raw 172.17, sp gr 2.31-2.33, white substance, mp loses 3/2HaO by 128° and rest by 167° hardness 1.5 to 2. Occurs naturally in the USA, Canada, England, France, Sicily, Switzerland etc si sol in w sol in acids, glycerin and aqueous Na3S2Oa and ammonium salts... 

The hardness of sodium chloride is nearly 2, and it is a little harder than gypsum. The hardness of a cubic face of the crystal is less than that of an octahedral face and the hardness of a dodecahedral is intermediate between the two. 

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