ドロマイト

ドロマイト 化学特性,用途語,生産方法

• 定義

  ドロマイト,三方晶系に属する鉱物で，理想的化学組成は CaMg(CO3)2 で複炭酸塩。色は白，灰色などを呈し，ガラス光沢がある。劈開は {1011} に完全。比重約 2.9 ，硬度 3.5～4 。日本名で苦灰石，白雲石などと呼ばれる。なお，正しくはドロマイトは鉱物名であるが，この鉱物を含む岩石としても用いられている。石灰岩などを伴って，堆積岩として広く産出する場合と，塩基性岩中や鉱脈中に産出する場合がある。堆積性のものの成因については異論が多い。製鉄用材料その他利用価値が大きい。フランスの鉱物学者 D.ドロミューにちなみ命名。

• 定義

  本品は、次の化学式で表される鉱物の一種、苦灰石である。

• 性質

  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3"2/mから3"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R3，りょう面体，双晶面{0001}，へき開{10¹"1}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 FeⅡ，MnⅡ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．
  森北出版「化学辞典（第2版）

• 解説

  炭酸塩鉱物，CaMg(CO₃)₂．水に不溶の無色結晶．日本語では苦灰石あるいは白雲石という．通常，石灰岩に伴って産する．

• 用途

  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．

• 化粧品の成分用途

  不透明化剤、研磨.スクラブ剤

• 説明

  Dolomite is a massive calcareous sedimentary rock made of the mineral dolomite [CaMg(CO₃)₂, rhombohedral]. Usually dolomite as a rock contains, apart from dolomite, other carbonates (e.g., calcite, magnesite, and siderite), along with some silica and alumina, mostly as clays. For commercial purposes, the mass fraction of combined impurities must be below 7 wt.%, above which it becomes unsuitable for industrial use and is then used only for road ballasts and building stones. When the percentage of calcium carbonate (CaCO₃) is above 10 wt.% or more over the theoretical composition, the rock is termed calcitic dolomite, while with a departure from theoretical magnesite content the rock is called dolomitic limestone. With variations in MgCO₃ between 5 and 10 wt.%, it is called magnesian limestone, and when it contains up to 5 wt.% MgCO₃ or less it is considered limestone for all purposes.

• 物理的性質

  Habit: rhombohedral, crystalline, massive, botryoidal, globular, stalactitic.
  Color: white, gray, reddish white, brownish white, or gray.
  Luster: vitreous (i.e., glassy).
  Diaphaneity: transparent to translucent.
  Streak: white.
  Cleavage: (1011) perfect.
  Twinning: {0001}, {1010}, {1110}, {0112}.
  Fracture: brittle, subconchoidal.
  Chemical: readily dissolved by strong mineral acids with evolution of carbon dioxide.
  Occurrence: sedimentary rocks.

• 定義

  dolomite: A carbonate mineral consistingof a mixed calcium–magnesiumcarbonate, CaCO₃.MgCO₃,crystallizing in the rhombohedralsystem. It is usually white or colourless.The term is also used to denotea rock with a high ratio of magnesiumto calcium carbonate. See limestone.

• 农业用途

  Dolomite is a carbonate of calcium and magnesium. It is a mineral of formula CaMg(CO₃)₂ with a rhombohedral system. It has a density of 2.8 g/cc and hardness of 4 on the Mohs scale.
  Dolomite has a vitreous lustre which is between transparent and translucent. It effervesces with hot concentratedh ydrochloric acid (HCl).
  A carbonate-rich sedimentary rock of chemical or biological origin contains 50% or more carbonate, of which at least half is in the form of dolomite. The color of dolomite is darker than limestone and does not give any effervescence with cold and dilute HCl.
  Dolomite may also contain iron and manganese. Depending on the proportion of dolomite and calcite, there are many transitional phases between calcareous dolomites and dolomitic limestones.
  Dolomite has multiple applications. It is used in the manufacture of magnesium and its compounds. It is also used as building material, as a refractory for furnaces, as a fertilizer, for the removal of sulphur dioxide from stack gases and in ceramics.

• 工業用途

  Dolomite is the carbonate mineral CaMg(CO3)2,often with small amounts of iron, manganese,or excess calcium, which replace some of themagnesium; cobalt, zinc, lead, and barium aremore rarely found.
  Dolomite is a very common mineral, occurringin a variety of geologic settings. It is oftenfound in ultrabasic igneous rocks, notably incarbonates and serpentinites, in metamorphosedcarbonate sediments, where it may recrystallize to form dolomite marbles, and inhydrothermal veins. The primary occurrence ofdolomite is in sedimentary deposits, where itconstitutes the major component of dolomiterock and is often present in limestones.
  Dolomite is normally white or colorlesswith a specific gravity of 2.9 and a hardness of3.5-4 on Mohs scale.

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