A gemstone is a naturally occurring, inorganic solid with a crystalline structure. It's typically beautiful and durable enough to be used in jewelry or other decorative objects. While many minerals can be gemstones, only those with desirable properties like color, brilliance, and rarity are usually considered such.

Gemstones form through a variety of geological processes, including:

• Magmatic processes: Crystals form within cooling magma or lava.
• Hydrothermal processes: Hot, mineral-rich water circulates through cracks in the Earth's crust, depositing crystals.
• Metamorphic processes: Existing rocks are transformed by heat and pressure, creating new minerals, including gemstones.
• Sedimentary processes: Gemstones can be formed through the accumulation and cementation of mineral grains.

The value of a gemstone is determined by several factors, often summarized by the "4Cs":

• Cut: How well the gemstone is shaped and polished to enhance its brilliance and beauty.
• Clarity: The absence of inclusions (internal flaws) and blemishes (external flaws).
• Carat: The weight of the gemstone, with one carat equaling 200 milligrams.
• Color: The hue, saturation, and tone of the gemstone's color. This can vary widely depending on the specific gemstone. Rarity also plays a significant role. For example, a perfectly clear, deep blue sapphire is more valuable than a pale, cloudy one.

Some of the most popular gemstones include diamonds, sapphires, rubies, emeralds, and pearls (though technically an organic gem). Many other gemstones, such as amethyst, garnet, topaz, and opal, are also highly valued and sought after.  

Proper care extends the lifespan and beauty of your gemstones. Recommendations vary depending on the gemstone:

• Cleaning: Gentle cleaning with warm soapy water is usually suitable for most stones. Avoid harsh chemicals or abrasive cleaners.
• Storage: Store gemstones separately in soft cloths or pouches to avoid scratching.
• Wearing: Remove jewelry before engaging in activities that could damage gemstones (e.g., household chores, sports).
• Insurance: Consider insuring valuable gemstones against loss or damage.

The distinction between "gemstone" and "semi-precious stone" is largely outdated and arbitrary. Historically, it was based on rarity and value, with "precious" typically referring to diamonds, rubies, sapphires, and emeralds. However, many "semi-precious" stones are now highly valued and even more rare than some stones previously considered "precious." The terms are often used interchangeably or avoided altogether by professional gemologists.