Examples of silicates are olivine, quartz, almandine, zircon, topaz and beryl. Silicates are materials that contain silicon dioxide, SiO2 or SiO4. Silicon dioxide is the most abundant material in the Earth's crust.
Olivine is a mineral made of magnesium iron silicate. It comes in stubby, prismatic crystals that are olive green to yellowish. Olivine is heavy and hard, though it is fragile. Nearly all olivine found on Earth is a type called forsterite. This includes peridot, which is worn as a gem.
Quartz makes up much of the sand that's found on Earth. It can be found in masses or in crystals that can be quite large. When it's pure, quartz is transparent and is called rock crystal. However, impurities lend it a great variety of colors. Types of quartz include the purple amethyst, citrine and aventurine.
Almandine, which is iron aluminum silicate, belongs to the garnet group. It is found as well-formed crystals and can be bright or dark red. Like olivine, it is heavy and hard, yet fragile, and it breaks into splinters.
Zircon, which is zirconium silicate, is also found in stubby, prismatic crystals. Its colors can range from colorless to yellow, brown, red, gray or green. It's often found in igneous rocks.