Olivine

Olivine is a silicate mineral with the general composition (Mg,Fe)₂SiO₄. Having a very high crystallization temperature, it is formed early in the Bowen reaction series. It has no cleavage planes and is black to dark green in color. The absence of cleavage planes contributes to a glassy appearance, and any fractures will be conchoidal rather than smooth and planar. The dark color is associated with the high content of iron and magnesium, making olivine an example of a "ferromagnesian" mineral.

橄榄石是一种含硅酸盐的矿物，其一般化学式为(Mg,Fe)₂SiO₄。它具有非常高的结晶温度，在伯恩斯反应系列中较早形成。它没有解理面，颜色为黑色至暗绿色。缺乏解理面导致其呈现出玻璃状外观，任何裂隙都将是锥形而非平滑的。暗色与铁和镁含量高有关，使橄榄石成为一种“铁镁质”矿物的例子。

Though not abundant in continental rocks, olivine is yet thought to be a major component of the upper mantle of the Earth. Part of the basis for this presumption is the fact that it is one of the first minerals to crystallize from molten magma.

尽管在大陆岩石中并不丰富，橄榄石仍被认为是地球上地幔的主要成分之一。这一假设的基础之一是，它是在熔融岩浆中首先结晶的矿物之一。

In Olivine the Fe²⁺ and Mg²⁺ freely substitute for each other. The Fe²⁺ and Mg²⁺ ions have almost the same size, 0.074 nm and 0.066 nm respectively, so the substitution makes very little structural change. The chemical formula (Mg,Fe)₂SiO₄ implies any mixture of iron and magnesium. It is said to be a "family" of minerals rather than one which has a definite composition.

在橄榄石中，Fe²+和Mg²+离子可以互相替代。Fe²+和Mg²+离子的尺寸几乎相同，分别为0.074 nm和0.066 nm，因此这种替代对结构造成的影响很小。化学式(Mg,Fe)₂SiO₄表明其中可以含有铁和镁的任意混合物。它被称作一种‘矿物族’，而不是具有固定组成的单一矿物。