只有一分钟的演讲没有时间详细讨论,因此必须做出归纳,经过仔细观察,并不完全正确。这* *是正确的,大多数的沙子是由石英构成,这大部分石英起源于风化granitie岩石,其中主要矿物有石英、钾长石和斜长石,通常用一些云母,很少一些角闪石和几乎从不橄榄石。在岩浆橄榄石和石英反应使角闪石(如果这是一个非常含水熔体)或辉石。可以找到一个沉积岩风化的石英和长石颗粒。根据原化学可以富含钾长石(正长石)或sodium-calcium-rich(斜长石)。由此产生的沉积岩被称为一个长石砂岩。长石砂岩是常见的侵蚀花岗岩在干旱地区,如撒哈拉以南非洲的干燥器部分。然而,它是更普遍的风化涉及湿侵蚀——成千上万的雨和太阳周期,热,冷,在这种情况下,长石组成主要是分解粘土(许多品种和亚种)。橄榄石是更基本的火山岩的特征,特别是玄武岩,天气不屈服石英颗粒。另一个岩石ntype橄榄岩中橄榄石是一种主要组件。 This weathers to yield goethite (a kind of ironstone) and serpentine. Occasionally, if the pyroxene to olivine ratio is sufficiently high, the weathering can yield quartz as a secondary by-product. Another feature of quartz: Over long periods and especially at high temperatures and/or high pressures, it is very slightly soluble. Not that you would notice. The sand isn't going to dissolve beneath your feet, but every litre of surface water contains a few milligrams of dissolved quartz as silicic acid, which takes part in a whole catalogue of geological processes. In addition, there are many other rocks besides quartz which yield quartz grains, including quartzite, weathered pre-existing sandstone, schist, gneiss, and some intermediate rocks (complex chemistry between granite and basalt. Even limestone - rocks that are generally thought of as 'pure' calcium carbonate, generally have a percent or two of insoluble residue, of which quartz is the dominant component.