Calcium Sulfate
<p><b >Calcium sulfate</b> (or calcium sulphate) is a common laboratory and industrial chemical. In the form of γ-<a href="http://en.wikipedia.org/wiki/Anhydrite" title="Anhydrite" >anhydrite</a>(the nearly <a href="http://en.wikipedia.org/wiki/Anhydrous" title="Anhydrous" >anhydrous</a> form), it is used as a <a href="http://en.wikipedia.org/wiki/Desiccant" title="Desiccant" >desiccant</a>. It is also used as a <a href="http://en.wikipedia.org/wiki/Flocculation" title="Flocculation" >coagulant</a> in products like <a href="http://en.wikipedia.org/wiki/Tofu" title="Tofu" >tofu</a>.<sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Calcium_Sulfate#cite_note-4" >[5]</a></sup> </p>
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In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock. When sold as a color-indicating variant under the name <a href="http://en.wikipedia.org/wiki/Drierite" title="Drierite" >Drierite</a>, it appears blue or pink due to impregnation with <a href="http://en.wikipedia.org/wiki/Cobalt(II)_chloride" title="Cobalt(II) chloride" >Cobalt(II) chloride</a>, which functions as a moisture indicator. </p>
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The <a href="http://en.wikipedia.org/wiki/Hydrate" title="Hydrate" >hemihydrate</a> (CaSO<sub >4</sub>·0.5H<sub >2</sub>O) is better known as <a href="http://en.wikipedia.org/wiki/Plaster_of_Paris" title="Plaster of Paris" class="mw-redirect" >plaster of Paris</a>, while the <a href="http://en.wikipedia.org/wiki/Hydrate" title="Hydrate" >dihydrate</a>(CaSO<sub >4</sub>·2H<sub >2</sub>O) occurs naturally as <a href="http://en.wikipedia.org/wiki/Gypsum" title="Gypsum" >gypsum</a>. </p>
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The anhydrous form occurs naturally as <a href="http://en.wikipedia.org/wiki/Anhydrite" title="Anhydrite" >β-anhydrite</a>. Depending on the method of calcination of calcium sulfate dihydrate, specific hemihydrates are sometimes distinguished: alpha-hemihydrate and beta-hemihydrate.<sup id="cite_ref-t_5-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Calcium_Sulfate#cite_note-t-5" >[6]</a></sup> They appear to differ only in <a href="http://en.wikipedia.org/wiki/Crystal" title="Crystal" >crystal</a> size. Alpha-hemihydrate crystals are more prismatic than beta-hemihydrate crystals and, when mixed with water, form a much stronger and harder superstructure.<sup id="cite_ref-6" class="reference" ><a href="http://en.wikipedia.org/wiki/Calcium_Sulfate#cite_note-6" >[7]</a></sup></p>