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GEM STONES

Lapis lazuli (sometimes abbreviated to lapis) is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color. Lapis takes an excellent polish and can be made into jewelry, carvings, boxes, mosaics, ornaments, and vases. It was also ground and processed to make the pigment ultramarine for tempera paint and, more rarely, oil paint. Its usage as a pigment in oil paint ended in the early 19th century when a chemically identical synthetic variety, often called French ultramarine, became available. In ancient Egypt, lapis lazuli was a favorite stone for amulets and ornaments such as scarabs; it was also used in ancient Mesopotamia by the Sumerians, Akkadians, Assyrians, and Babylonians for seals and jewelry. In the Epic of Gilgamesh; the oldest known story in human history, lapis lazuli is referenced several times. Lapis jewelry has been found at excavations of the Predynastic Egyptian site Naqada (3300–3100 BC), and powdered lapis was used as eyeshadow by Cleopatra. In ancient Mesopotamia, lapis artifacts can be found in great abundance, with many notable examples having been excavated at the 25th-century BC Statue of Ebih-Il, discovered in ancient Mari in Syria, uses lapis lazuli inlays that were imported from as far east as Afghanistan. In ancient times, lapis lazuli was known as sapphire, which is the name that is used today for the blue corundum variety sapphire. It has also been used in the Taj Mahal in India.

 

Tiger's Eye is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown color, with a silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite (blue asbestos). An incompletely silicified blue variant is called Hawk's eye.

 

MINERALS

Iceland Spar, formerly known as Iceland crystal, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light. It occurs in large readily cleavable crystals, easily divisible into rhombs, and is remarkable for its double refraction. Historically, the phenomena of this crystal were studied at length by Christiaan Huygens and Isaac Newton. Sir George Stokes also studied the phenomenon. It has been speculated that the sunstone mentioned in medieval Icelandic texts was Iceland spar and that Vikings used its light-polarizing property to tell the direction of the sun on cloudy days, for navigational purposes. In 2007, Ramón Hegedüs and his colleagues from Eötvös Loránd University in Budapest, Hungary, confirmed that the polarization of sunlight in the Arctic can be detected under cloudy conditions. Their research is reported in "The Proceedings of the Royal Society." Further research in 2011 by Ropers et al., confirms that identifying the direction of the sun to within a few degrees in both cloudy and twilight conditions was possible using the sunstone and the naked eye. The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye, probably Haidinger's brush. The recovery of an Iceland spar sunstone from the Elizabethan ship Alderney that sank in 1592 suggests that the navigational technology may have persisted after the invention of the magnetic comp

 

Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz, several of which are semi-precious gemstones. Especially in Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings. The word "quartz" is derived from the German word "Quarz" and its Middle High German ancestor "twarc", which probably originated in Slavic (cf. Czech tvrdy ("hard"), Polish twardy ("hard")).

 

Citrine is a variety of quartz whose color ranges from a pale yellow to brown. Natural citrines are rare; most commercial citrines are heat-treated amethysts or smoky quartzes. It is nearly impossible to tell cut citrine from yellow topaz visibly, but they differ in hardness. Citrine has ferric impurities, and is rarely found naturally. Brazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul. The name is derived from Latin citrina, which means "yellow" and is also the origin of the word "citron." Sometimes citrine and amethyst can be found together in the same crystal, which is then referred to as ametrine. Citrine is one of three traditional birthstones for the month of November.

 

Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek ἀ a- ("not") and μέθυστος methustos ("intoxicated"), a reference to the belief that the stone protected its owner from drunkenness. The ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication. It is one of several forms of quartz. Amethyst is the traditional birthstone for February.

 

Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black. On exposure to air, chalcopyrite oxidises to a variety of oxides, hydroxides and sulfates. Associated copper minerals include the sulfides bornite (Cu5FeS4), chalcocite (Cu2S), covellite (CuS), digenite (Cu9S5); carbonates such as malachite and azurite, and rarely oxides such as cuprite (Cu2O). Chalcopyrite is rarely found in association with native copper.

 

Kyanite, whose name derives from the Greek word kuanos sometimes referred to as "kyanos", meaning deep blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. Kyanite in metamorphic rocks generally indicates pressures higher than 4 kilobars. Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such as muscovite, pyrophyllite, or kaolinite. Kyanite is also known as disthene, rhaeticite and cyanite. Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dishware. It is also used in electronics, electrical insulators and abrasives. Kyanite has been used as a semiprecious gemstone, which may display cat's eye chatoyancy, though this use is limited by its anisotropism and perfect cleavage. Color varieties include recently discovered orange kyanite from Tanzania. The orange color is due to inclusion of small amounts of manganese (Mn3+) in the structure. Kyanite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism.

 

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a specific gravity of 2.71, and its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities. Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar"

 

Chrysocolla The name comes from the Greek chrysos, "gold", and kolla, "glue", in allusion to the name of the material used to solder gold, and was first used by Theophrastus in 315 BCE. It is of secondary origin and forms in the oxidation zones of copper ore bodies. Associated minerals are quartz, limonite, azurite, malachite, cuprite, and other secondary copper minerals.

It is typically found as botryoidal or rounded masses and crusts, or vein fillings. Because of its light color, it is sometimes confused with turquoise.

 

Lepidolite is a lilac-gray or rose-colored member of the mica group that is a secondary source of lithium. It is a phyllosilicate mineral and a member of the polylithionite-trilithionite series. It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the rare alkali metals rubidium and caesium. In 1861 Robert Bunsen and Gustav Kirchhoff extracted 150 kg of lepidolite and yielded a few grams of rubidium salts for analysis, and therefore discovered the new element rubidium. It occurs in granite pegmatites, in some high-temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.

Notable occurrences include Brazil; Ural Mountains, Russia; California, United States; Tanco Mine, Bernic Lake, Manitoba, Canada; and Madagascar.

 

Carnelian (also spelled cornelian) is a brownish-red mineral, which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker (the difference is not rigidly defined, and the two names are often used interchangeably). Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide. The color can vary greatly, ranging from pale orange to an intense almost-black coloration.

 

Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur. Typical malachite is laminated and whether or not microbes intervene in its formation is unknown.

 

Fluorite (also called fluorspar) is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Crystal twinning is common and adds complexity to the observed crystal habits. The word fluorite is derived from the Latin root fluo, meaning "to flow" because the mineral is used as a flux in iron smelting to decrease the viscosity of slags at a given temperature. This increase in fluidity is the result of the ionic nature of the mineral. The melting point of pure calcium fluoride is 1676 K. In 1852 fluorite gave its name to the phenomenon of fluorescence, which is prominent in fluorites from certain locations, due to certain impurities in the crystal. Fluorite also gave the name to its constitutive element fluorine. Fluorite is a colorful mineral, both in visible and ultraviolet light, and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so lenses made from it exhibit less chromatic aberration, making them valuable in microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet range where conventional glasses are too absorbent for use.

 

Pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale brass-yellow hue have earned it the nickname fool's gold because of its superficial resemblance to gold. The color has also led to the nicknames brass, brazzle and Brazil, primarily used to refer to pyrite found in coal. Pyrite is the most common of the sulfide minerals. The name pyrite is derived from the Greek πυρίτης (puritēs), "of fire" or "in fire", in turn from πύρ (pur), "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite. By Georgius Agricola's time, the term had become a generic term for all of the sulfide minerals. Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds, and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold.

 

FOSSILS

Ammonite- The name comes from its appearance: it resembles a ram’s horn. In Egyptian mythology, the God Ammon looked like a man with horns like a ram. The ancient fossil was considered Ammon’s stone, thus inheriting the name, ammonite. Ammonites have a wide range of size. Specimens have been found ranging from less than a centimeter to two meters in diameter. Early ammonites, until the middle Jurassic, were smaller, usually less than nine inches or 23 centimeters.

 

Brachiopods are benthic (bottom dwelling), marine (ocean), bivalves (having two shells). They are considered living fossils, with three orders present in today’s oceans. They are rare today but during the Paleozoic Era they dominated the sea floors. Though they appear to be similar to clams or oysters they are not related. They are not even mollusks. They belong to the phylum Lophophorata and are related to bryozoans. One characteristic unique to brachiopods is the pedicle. It is a long thin fleshy appendage. The pedicle is used to burrow into the sea floor as an anchor. Some Brachiopods have a muscular pedicle. They can raise themselves up off the bottom, looking like they are standing on their heads. For others it is more like a tether. Not all orders have a pedicle. Some lay on the sand on one side. With these the bottom shell is usually larger than the top shell. There are even some types that cement themselves to the ocean floor.

 

Orthoceras was an ancient mollusk that lived more than 400 million years ago. The name means straight horn, referring to the characteristic long, straight, conical shell. The preserved shell is all that remains of this ancestor of our modern-day squid. These straight shelled nautiloids ranged in size from less than a centimeter to more than 14 feet long! All the living relatives of these nautiloids, squid, octopus, cuttlefish, and nautilus are predators, and we can assume that orthoceras was also a hunter of the Paleozoic seas, possibly having trilobites for breakfast!

 

MISC

Tektites (from Greek τηκτός "tēktos", molten) are gravel-size bodies that are composed of black, green, brown or gray, natural glass that are formed from terrestrial debris ejected during extraterrestrial impacts. They are characterized by 1.) a fairly homogeneous composition; 2.) an extremely low content of water and other volatiles; 3.) an abundant lechatelierite; 4.) a general lack of microscopic crystals known as microlites and chemical relation to the local bedrock or local sediments; and 5.) their distribution within geographically extensive strewnfields. Tektites generally range in size from centimeters to millimeters. Millimeters-size tektites are known as microtektites.

 

Although tektites are superficially similar to some terrestrial volcanic glasses (obsidians), they have unusual distinctive physical characteristics that distinguish them from such glasses. First, they are completely glassy and lack any microlites or phenocrysts unlike terrestrial volcanic glasses. Second, although high in silica (>65 wt%), the bulk chemical and isotopic composition of tektites is closer to those of shales and similar sedimentary rocks and quite different from the bulk chemical and isotopic composition of terrestrial volcanic glasses. Third, tektites contain virtually no water (<0.02 wt%) unlike terrestrial volcanic glasses. Fourth, the flow-banding within tektites often contains particles and bands of lechatelierite, which are not found in terrestrial volcanic glasses. Finally, a few tektites contain partly melted inclusions of shocked and unshocked mineral grains, i.e. quartz, apatite, and zircon, as well as coesite.

 

 

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