A gemstone is any rock or mineral that could be used for ornamentation or jewelry. Gemstones usually are minerals prized for their color, beauty, rarity, and endurance. Most often, the minerals are cut and polished to bring out the natural beauty of the piece. Even diamonds must be cut into their familiar faceted shapes to really sparkle (uncut versus cut shown below). Colorado has over many varieties of gems and ornamental stones, including diamonds, rhodochrosite and aquamarine.
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 rated as a 10 on the Mohs Scale of Hardness which ranges from 1-10. That means diamonds will scratch all other minerals and those minerals can’t scratch it. Rubies and sapphires — different colors of the mineral corundum — are a 9 on the Mohs scale. Emeralds and aquamarines — different colors of the mineral beryl — come in at 8 on the scale.
Lots of generic dust is composed of minerals with hardnesses of around 6 and 7. Because of this, any minerals less than a hardness of 6, 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 a typical 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 varieties of gemstones. The largest faceted diamond produced in the United States (16.87 carats) was found in Colorado. The official state gemstone is aquamarine, a beautiful blue mineral mostly found around the 13,000 foot 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.