菱镁矿的成因 Origin of magnesite

http://www.ykbhlm.com 菱镁矿的成因主要有二。其一，外生成因，产自沉积岩中：这些层状的碎屑沉积岩大多带有来自生物的有机组份。换言之，菱镁矿是在低氧的情况下藉生物作用形成；其二，形成于中温至低温的热液矿脉内：菱镁矿常见于变质沉积岩中，是热液堆积后形成的脉石矿物；此外，伟晶岩中亦可能出现菱镁矿。

其常见的共生矿物有：石英、黄铁矿（pyrite）、褐铁矿（limonite）、针铁矿（goethite）、黄铜矿（chalcopyrite）、闪锌矿（sphalerite）、冰晶石（cryolite）、方铅矿（galena）、重晶石（barite）、方解石、白云石（dolomite）、萤石（fluorite）等。由于各矿物的结晶构造相似，因此它们具许多相似的物理性质，包括：属于三方晶系、（trigonal）－－晶型多为菱面体或scalenohedron，有三组发育优良的菱面体解理，透明菱面体结晶具有双折射（doublerefraction）现象等。实际上，矿物组成中的阳离子之间，彼此可以完全地相互取代，形成一系列的固溶液（solidsolution），因此矿物之间的分辨可能变得较为困难。

http://www.ykbhlm.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.