What are the most common types of crystals?

Here are some common types of crystals found in nature:

1. Quartz: One of the most common minerals on Earth, quartz comes in different varieties such as clear rock crystal, amethyst (purple), rose quartz (pink), citrine (yellow), and smoky quartz (gray-brown).
2. Feldspar: A group of abundant rock-forming minerals, including orthoclase, plagioclase, and microcline. They are important components of many igneous and metamorphic rocks.
3. Mica: Another group of rock-forming minerals with a sheet-like structure. Biotite (black mica), muscovite (white mica), and phlogopite (brown mica) are common varieties.
4. Calcite: A carbonate mineral that is a major component of limestone, marble, and chalk. It comes in various colors and forms, such as transparent Iceland spar, stalactites and stalagmites in caves, and the double-refracting calcite crystals used in optical devices.
5. Dolomite: A carbonate mineral similar to calcite but contains both calcium and magnesium. It is often found in association with limestone and is used as a building material and in the production of cement.
6. Halite (Rock Salt): Composed primarily of sodium chloride (NaCl), halite is the mineral form of common table salt. It crystallizes in cubic shapes and is found in evaporite deposits.
7. Gypsum: A sulfate mineral that forms in sedimentary environments. It is commonly used in construction as drywall, plaster of Paris, and as an agricultural soil amendment.
8. Pyrite ('Fool's Gold'): An iron sulfide mineral that has a brassy, yellow color and metallic luster. While it resembles gold, it is much softer and has a distinct cubic crystal form.
9. Garnet: A group of silicate minerals that come in various colors, including red, orange, green, and purple. Garnets are often used as gemstones and abrasives.
10. Amethyst: A variety of quartz that gets its purple color from impurities of iron and manganese. It is one of the most popular and widely used gemstones.
11. Topaz: A silicate mineral that comes in a variety of colors, including yellow, blue, pink, and colorless. It is used as a gemstone and is known for its hardness and durability.

These are just a few examples of the numerous crystal types that occur naturally. Each crystal has unique properties and may be sought after for its aesthetic appeal, geological significance, or practical uses.