菱鎂礦的成因 Origin of magnesite

http://www.chinaqdzhenhua.com 菱鎂礦的成因主要有二。其一，外生成因，產自沉積巖中：這些層狀的碎屑沉積巖大多帶有來自生物的有機組份。換言之，菱鎂礦是在低氧的情況下藉生物作用形成；其二，形成于中溫至低溫的熱液礦脈內：菱鎂礦常見于變質沉積巖中，是熱液堆積后形成的脈石礦物；此外，偉晶巖中亦可能出現菱鎂礦。

其常見的共生礦物有：石英、黃鐵礦（pyrite）、褐鐵礦（limonite）、針鐵礦（goethite）、黃銅礦（chalcopyrite）、閃鋅礦（sphalerite）、冰晶石（cryolite）、方鉛礦（galena）、重晶石（barite）、方解石、白云石（dolomite）、螢石（fluorite）等。由于各礦物的結晶構造相似，因此它們具許多相似的物理性質，包括：屬于三方晶系、（trigonal）－－晶型多為菱面體或scalenohedron，有三組發育優良的菱面體解理，透明菱面體結晶具有雙折射（doublerefraction）現象等。實際上，礦物組成中的陽離子之間，彼此可以完全地相互取代，形成一系列的固溶液（solidsolution），因此礦物之間的分辨可能變得較為困難。

http://www.chinaqdzhenhua.com There are two main causes for magnesite. First, exogenous factors are produced in sedimentary rocks: Most of these layered clastic sedimentary rocks carry organic components derived from organisms. In other words, magnesite is formed by biological action under low oxygen conditions. Second, it is formed in hydrothermal veins of moderate to low temperature: magnesite is commonly found in metamorphic sedimentary rocks and is a gangue mineral formed after hydrothermal accumulation. In addition, magnesite may also appear in pegmatite.

The common symbiotic minerals are: quartz, pyrite, limonite, goethite, chalcopyrite, sphalerite, cryolite, Galena, barite, calcite, dolomite, fluorite, etc. Because the crystalline structures of the minerals are similar, they have many similar physical properties, including: belonging to the trigonal system, (trigonal)-most of the crystal form is rhombohedron or scalenohedron, there are three groups of well-developed rhombohedron cleavage, transparent rhombus The facet crystal has a double refraction phenomenon and the like. In fact, the cations in the mineral composition can completely replace each other to form a series of solid solutions, so the discrimination between minerals may become more difficult.