summer 2016 GEMSTONES OF NEW MEXICO leasing colors, shapes, durability, production. Native people used a Pand rarity are all characteristics of number of gem materials (turquoise, the minerals that we call gemstones. shell, and jet) in their ceremonial The quest for these stones has long objects and gemstones, specifically allured people. Gemstones have been pyrope garnet (red, magnesium-rich found in many archeological sites, garnet) and peridot (pale green gem attesting to a long fascination with version of a mineral called olivine), beautiful objects from the earth. We which have been found in the ruins continue to decorate ourselves with of their dwellings. Native American these objects as an expression of jewelry style is still based on the use status, or simply to enjoy something of turquoise and other stones, often beautiful. Many gemstones have a set in silver or strung in necklaces. long and complicated path from However, the most well-known where they are formed, in the earth, precious gems, diamond, emerald, to finally becoming a necklace, ring, ruby, and sapphire are poorly rep- pin, or other type of adornment. resented in the state. Semiprecious Gemstones are minerals that stones like quartz and its varieties have clarity (containing little to (amethyst, citrine, smoky or rose), no material interfering with the feldspar (the most common mineral passage of light), color (a desirable in the earth’s crust), peridot, and hue, saturation, & tone), and a level beryl (a beryllium-rich mineral) are of hardness that resists abrasion more abundant. Turquoise is, by or chipping. When we think of far, the most iconic New Mexico gemstones, we typically think of gemstone/gem material, as well as diamond, emerald, ruby, or sapphire, the classic, Kelly blue smithsonite which are cut (faceted) and placed in (bottom photo). A thorough discus- rings, pendants, pins, and earrings sion of these minerals is beyond (top photo). However, another class of the scope of this article, so we will gems, called gem materials, includes focus on other gemstones and rocks or minerals that lack the clarity gem materials from the Land of and sparkle of gemstones, but are Enchantment. used for adornment because of pleasing color or pattern. Turquoise, Historical Accounts of malachite, jasper, and other colored Gems in New Mexico rocks and minerals represent gem Top—Gemstones cut & polished for jewelry, from the Mineral When the Spanish conquistadors materials, which are usually carved Museum gemstone collection. Back row, left to right: amethyst, explored New Mexico, they were citrine, rose quartz, topaz; middle row, left to right: aquamarine, or “cabbed”, worked into a disk or elbaite, chrysoberyl; front row, left to right: heliodor, rubellite, seeking gold, silver, and gemstones. oblong smooth oval object called a spessartine. A number of their reports mention cabochon (bottom photo). Bottom—Popular gem materials used in carvings, slabs, & the presence of gemstones, usually cabochons, from the Mineral Museum gemstone & mineral highlighting their abundance Introduction collection. Back row, left to right: smithsonite sphere, calcite onyx slab; middle row, left to right: ricolite cabochon, Apache (showing that exaggeration is not New Mexico is blessed with a picture rhyolite slab, red agate cabochon; front row, left to right: something invented by modern wide variety of gemstones and has turquoise cabochon, malachite/azurite cabochon, lepidolite advertisers!). One of the first a long history of gemstone use and teardrop cabochon. Photos by Virgil Lueth. accounts was by Cabeza de Vaca, Published by the New Mexico Bureau of Geology and Mineral Resources • A Division of New Mexico Tech Bedded Large-scale production found above diatreme vents. Erosion pyroclastics of gemstones and gem following the eruption can expose the material has been attempted diatreme as a high-standing landform, a Maar in New Mexico, particularly well-known example in New Mexico being for turquoise. There has Shiprock. Peridot, red pyrope garnet, and been a general lack of bright green chrome diopside are the most systematic exploration for other types of common examples of diatreme-related Diatreme gemstone deposits because the costs of gems in New Mexico. The Navajo Volcanic development usually are greater than any Field on the Navajo Nation* has numerous indicated profit from production. occurrences of these gems. Peridot, pyrope, Breccia The small size of the deposits, and chrome diopside weather from the capricious distribution and host rock, called peridotite, and accumulate quality of stones, and on the surface or are concentrated on ant market demands conspire hills by the industrious insects. The gems to make New Mexican can be easily collected, and are packaged gem mining only a and sold in local trading posts. At these gift small scale affair. Most shops, the gems are often given fanciful deposits in our state are names like, “emerald, beryl, green garnet found and developed or Job’s tears” for peridot, and “Arizona, by mineral collectors or Rocky Mountain, or New Mexico rubies” weekend gem hunters. for pyrope. Another famous peridot locality is Schematic diagram of a funnel-shaped Gemstone Deposits of Kilbourne Hole, a maar crater in the diatreme at depth and a broad shallow crater, Potrillo Volcanic Field of Doña Ana or maar, at the surface. Shiprock represents New Mexico an exposed portion of a diatreme, while County*. At Kilbourne Hole, fragments Kilbourne Hole is an excellent example of a Gemstones form in a wide variety of of volcanic rocks, called bombs, that were maar. Photo shows xenocrysts of light green environments, from the earth’s partially ejected from the vent during a very ener- olivine (peridot) and dark green chrome molten mantle, to the earth’s surface, getic and explosive eruption, can include diopside that were carried from the mantle through alteration of volcanic rocks. peridot xenocrysts (diagram upper left). to the surface during an explosive eruption. The unique environments that allow Specimen is 8 cm across. Photo by Shari Kelley. These bombs are scattered about the crater gemstones to form in the earth’s crust and and have been collected for over 100 years. describing emeralds shaped like arrow mantle result in their rarity. A multitude A rather unique occurrence of volcanic- points. Quartz crystals known as “Pecos of physical processes and conditions (e.g. related gemstones can be found at Pueblo Valley diamonds” were first described by temperature & pressure regime, presence Park in Catron County*. Hosted in a Don Antonio de Espejo in 1583. Carrera or absence of fluids, trace elements, etc.) basalt lava flow are large, clear, yellow reported the presence of “lapis lazuli” in must combine in particular ways in order to crystals of calcium-rich plagioclase feldspar the Organ Mountains that turned out to produce a beautiful gemstone. Gemstones that grew in the magma chamber from be another blue mineral, lazulite. Reports can be grouped, or classified, based on their which the basalt was erupted. These stones, of emeralds, rubies, and diamonds, all environment of formation. Several such formally known as labradorite, have been misidentified, persisted through the environments, which will be defined and collected and faceted by gem hunters only Mexican period and into statehood. discussed below, include—volcanic-related, fairly recently (probably only since the The first gem minerals advertised from pegmatitic, hydrothermal, metamorphic, 1960s), and were hence not mentioned in New Mexico, in early mineralogical maga- and sedimentary. In the following sections, the first two editions of Minerals of New zines, were peridot and pyrope. An article locations of gemstones marked with an Mexico. These gems are a pleasing honey- published in The Mineral Collector in asterick can be found on the map. yellow color, and a few rare stones display 1895 titled, “American Jewel Mines” touts a copper color similar to sunstones found New Mexico gem occurrences: “…The Volcanic-Related in Oregon. fine aquamarine beryl has also come quite Most volcanic-related gemstones Diamonds may be found in diatremes, extensively from Stoneham, Maine. This originate deep in the earth’s mantle. having been transported to the surface in gem, or rather mineral, abounds in New These crystals, called xenocrysts (foreign a similar way to the gemstones described Mexico and Arizona where it was mined by crystals), form at great depth 150–650 above. Diamonds are typically associated the early Aztecs, and later by the Spaniards kilometers (93–403 miles), and are carried with a rock type called kimberlite (a and Pueblo Indians. The demand for it is to the surface rapidly during very explosive potassic igneous rock), thought to erupt good and the supply never keeps pace with volcanic eruptions that form features from great depths extremely rapidly, the sales. The finest garnets in the world called diatremes and maars. Diatremes are possibly because the magma contained funnel-shaped volcanic throats, or con- come from these latter Territories. Peridots high concentrations of CO2, driving the are mined there, or rather taken from ant duits, filled with fragmented (brecciated) explosive eruption. Some magma composi- hills and scorpion nests by the Indians and volcanic rocks, as well as xenocrysts derived tions found in the Navajo Volcanic Field soldiers.” Once again it appears exaggera- from the mantle and/or rocks from the rocks are similar to kimberlites, but no tion transcends reality concerning New crust through which the magma erupted substantiated occurrence of diamond has Mexico gemstones. (diagram above). Maars are shallow craters ever been documented in New Mexico. new mexico earth matters 2 summer 2016 However, one of the first great gem hoaxes Raton of the west had a New Mexico connection, Tierra the Ralston diamond hoax (for more Amarilla information, please see the links provided at the end of this article). Pegmatites 25 Los Alamos Santa These rocks are very coarse-grained and Fe form during the last stages of magmatic Las Vegas Gallup crystallization or from high-grade meta- 40 Bernalillo morphism.