Dolomite

Japanese: ドロマイト

Also called dolomite or dolomite. A double carbonate of calcium and magnesium, CaMg(CO ₃ ) ₂ , or a rock composed mainly of this. It has a similar structure to calcite, but Mg is substituted for Ca, lowering the symmetry from 2/ m . It occurs as the main component of dolomite rock, forming layered deposits. In Japan, dolomite deposits are associated with limestone. In many cases, it is a secondary mineral formed by replacing CaCO _3. It is artificially obtained by keeping a solution of Ca and Mg carbonates at room temperature or higher under CO ₂ of 10 atm or more. Trigonal crystal system, space group R , rhombohedral, twin plane {0001}, perfect cleavage {101}. It often grows coaxially with calcite. Hardness 3.5-4. Density 2.85±0.01 g cm ^-3 . As the amount of Fe ^II and Mn ^II increases instead of Mg, the specific gravity, reflectivity, and refractive index increase. Biaxial, negative. Ca can be substituted for Mg up to a Ca:Mg ratio of 1:5, and Mg can be substituted for Ca up to a ratio of 1:20. When heated, _MgCO3 decomposes at around 800°C, and _CaCO3 decomposes at around 950°C, releasing _CO2 , resulting in a mixture of CaO and MgO. Its most common use is as a refractory for basic steelmaking, but it is also used in glass, pottery, and fertilizer. In Japan, lightweight pottery made primarily from dolomite is called Hakuun pottery.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Japanese:

苦灰石，白雲石ともいう．カルシウムとマグネシウムの複炭酸塩CaMg(CO₃)₂，またこれを主成分とする岩石．方解石と似た構造だが，Caの位置にMgが入るので対称が2/mからに下がる．ドロマイト岩の主成分鉱物として産出し，層状鉱床をつくる．わが国では，ドロマイト鉱床は石灰岩を伴っている．CaCO₃から交代してできた二次鉱物である場合が多い．人工的には，CO₂10 atm 以上のもとで，Ca，Mgの炭酸塩溶液を常温以上に保って得られる．三方晶系，空間群R，りょう面体，双晶面{0001}，へき開{101}完全．方解石と共軸成長している場合が多い．硬度3.5～4．密度2.85±0.01 g cm^－3．Mgのかわりに Fe^Ⅱ，Mn^Ⅱが増すにつれて，比重，反射率，屈折率が増加する．二軸性，負．MgのかわりにCaがCa：Mg ＝ 1：5まで，CaのかわりにMgが1：20まで置換する．加熱すると800 ℃ 付近でMgCO₃が，950 ℃ 付近でCaCO₃が分解してCO₂を放出し，CaOとMgOの混合物となる．最大の用途は塩基性製鋼用耐火物であるが，ガラスや陶器，あるいは肥料にも用いられる．ドロマイトを主原料とした軽量陶器を，わが国では白雲陶器と称している．