Posts Tagged ‘silicate materials’


Well, this blog is called “Star in the Stone” and that’s exactly what a pallasite is! How beautiful to reveal translucent gemstones welded into a molten mass. Peridot crystals can only be formed in outer space, brought down to earth in meteors.

There are three main types of meteorites.
Those made entirely of iron alloy, are thought to be the cores of asteroids that melted early in their history. They consist mainly of iron-nickel metal with small amounts of sulphide and carbide minerals. Iridium, is brittle, with a high melting point, similar to silver or platinum, an element very rare on earth, but often found in meteors. Most iron meteorites have a distinctive crystalline structure with bands containing low and high levels of nickel, known as Widmanstatten texture, which is highlighted when acid-etched.
Second, there are those meteorites made of an iron-stone blend, called pallasites. These consist of almost equal amounts of iron-nickel metal and silicate minerals, and are amongst the most beautiful of meteorites, because of the gemstones they contain. Pallasites contain big, beautiful olive-green crystals, a form of magnesium-iron silicate called olivine, embedded entirely in metal. Pallasites can show big variations. Sometimes the olivine does not occur as a single crystal but as a cluster and elsewhere it can create a pattern of veins through solid metal.
Third, are the stoney concretions, or chondrites, which consist mainly of silicate materials, such as olivine or feldspar, in conglomeration with iron or carbon. They are the most primitive meteorites in their chemical development. Chondrites come from asteroids that did not melt when formed. Carbonaceous chondrites often contain water-bearing minerals and compounds including the organic molecules such as amino acids, the building blocks of life on earth. Chondrites are the materials from which the solar system formed and have been little changed compared with rocks from the larger planets, which have been subjected to billions of years of geological activity. They are very similar in composition to the sun and can tell us a lot about how the solar system itself was formed. A variant of chondrite, called Achondrites include meteorites from asteroids, Mars and the moon. They are igneous, meaning that at some point they melted into magma. When the magma cools and crystallises, it creates a concentric layered structure, usually with metallic center and silicon coated exterior. This process is known as igneous differentiation,
which gave rocky planets of Mercury, Venus, Earth and Mars them planetary crusts, mantles and cores. Achondrites can, therefore, tell us a lot about the internal structure and formation of the planets.


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