Khoáng sản là các chất rắn tự nhiên hình thành đá. Một số bao gồm các yếu tố một, trong đó tất cả các nguyên tử đều giống nhau. Chúng bao gồm kim cương, dạng cacbon tinh khiết. Tuy nhiên, hầu hết hoặc nhiều khoáng chất là hợp chất của hai hoặc nhiều yếu tố. | MINERALS AND GEMSTONES Halite can be tinted by impurities Quartz can form big six-sided pyramidal crystals Diamond Rough diamond looks like glass Minerals are the natural solid substances that form rocks. A few consist of just one element in which all the atoms are the same. They include diamond a form of pure carbon. But most of the 4 000 or more known minerals are compounds of two or more elements. Quartz for example is a compound of silicon and oxygen. Most minerals can form crystals natural geometric shapes that reflect the way their atoms are bonded together. The crystals of some minerals are cut and polished into valuable gems. I HALITE Often known as rock salt halite is the same mineral as the salt used in cooking a compound of sodium and chlorine. Halite deposits found deep underground were created by the evaporation of salt water in ancient oceans. It forms cubic crystals that can often be found in coarse-ground table salt and is colorless when pure. o QUARTZ The most abundant mineral on Earth s surface quartz is one of the main ingredients of granite and similar hard rocks that have formed from molten magma. When these rocks are broken down by erosion the tough quartz crystals tend to survive as sand grains and these are used to make glass. Various colored forms of quartz such as purple amethyst are valuable gemstones. 4 OLIVINE Like quartz olivine is a mineral based on silica the compound of silicon and oxygen that is the basis of most rocks but it also contains iron and magnesium. It is more abundant than quartz but mostly below the crust because it is the main ingredient of the peridotite rock that forms much of the planet s deep mantle. Olivine crystals are usually green as seen here. 4 DIAMOND AND GRAPHITE Although they are both pure carbon diamond and graphite are physically very different. Diamond is the hardest of all minerals and a valuable gemstone while graphite is the soft streaky mineral used to make pencils. The difference is due to the way
