Gemstones usually are minerals prized for their color, rarity, and endurance. Endurance generally means that they are hard. Hard doesn't mean that they are hard to break, but that they are not easily scratched by other materials in the environment. Diamond is the hardest of all substances.
Diamond is 10 on the Mohs Scale of Hardness which ranges from 1-10. That means diamonds will scratch all other minerals and they can't scratch it. At 9 on the scale are rubies and sapphires which are different colors of the mineral corundum. At 8 are emeralds and aquamarines which are different colors of the mineral beryl. See a pattern developing?
Lots of dust is composed of minerals with hardnesses of 6 and 7. Therefore, any minerals less than a hardness of six, even though they can be quite beautiful, aren't suitable for gemstones because they do not have the endurance for their facets and polish to survive in our environment. They can easily be scratched by dust and other harder substances. Our mothers warned us not to put our drinking glass (hardness = 5.5) on her marble-topped table (hardness = 3) in the living room because the glass would scratch the polish on the table top. Most antique marble, table tops no longer have their original polish whereas antique diamond jewelry does.
Colorado has more than thirty different varieties of gemstone. The largest faceted diamond produced in the United States (16.87 carats) was found in Colorado. The official state gemstone is aquamarine, a beautiful mineral mostly found around 13,000 feet above sea level on Mount Antero. Other notable gem-quality minerals that have been found in Colorado include amazonite, garnet, topaz, tourmaline, lapis lazuli, quartz crystal, smoky and rose quartz, amethyst, turquoise, peridot, sapphire, and zircon. Agate, chalcedony, and jasper are found in many places.
Alabaster, a fine-grained, compact variety of gypsum used to make elegant vases and other decorative items, is quarried in the foothills northwest of Forth Collins and at a quarry south of Carbondale. However, it is not a gemstone because it is so soft (Mohs scale of 2). That is why it is easy to carve with steel tools.