Compounds of silicon and hydrogen, known as silanes, react explosively with oxygen and react with water, forming silicon dioxide and water and silicon dioxide and hydrogen gas respectively. Silicon accounts for 28 percent of the earth's crust but it does not appear naturally in its elemental form.
All silanes take the form of liquids or gases without color when observed at room temperature. In its pure elemental form, silicon is a lustrous gray substance, solid and very similar to a diamond in formation and appearance. In nature, it appears as silicon dioxide and as a great range of silicate minerals.
Only silane and disilane of the various silanes are stable on an indefinite basis. The various silicate minerals which appear in nature, including yellow beryl, quartz, beryl and amethyst are stable crystal formations which react nowhere near as regularly. They are too stable to undergo the kind of explosive reactions silanes do upon contact with oxygen and water.
The huge variety of silicates and silanes makes mapping their reactions a complex question. In general, there are predictable scenarios in which silanes will react and almost no scenarios in which silicates will react with common substances. This makes the element, while complicated, relatively easy to predict in its behaviors.