Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide with trace amounts of elements such as iron, chromium, copper, or magnesium. It is blue, but natural "fancy" sapphires occur in yellow, purple and green colors; the only color corundum stone that the term sapphire is not used for is red, called a ruby. Pink colored corundum may be either classified as sapphire depending on locale. Natural sapphires are cut and polished into gemstones and worn in jewelry, they may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale – sapphires are used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics. Sapphire is the gem of the 45th anniversary.
A sapphire jubilee occurs after 65 years. Sapphire is one of the two gem-varieties of the other being ruby. Although blue is the best-known sapphire color, they occur in other colors, including gray and black, they can be colorless. A pinkish orange variety of sapphire is called padparadscha. Significant sapphire deposits are found in Eastern Australia, Sri Lanka, Madagascar, East Africa, in North America in a few locations in Montana. Sapphire and rubies are found in the same geological setting; every sapphire mine produces a wide range of quality, origin is not a guarantee of quality. For sapphire, Kashmir receives the highest premium, although Burma, Sri Lanka, Madagascar produce large quantities of fine quality gems; the cost of natural sapphires varies depending on their color, size and overall quality. For gems of exceptional quality, an independent determination from a respected laboratory such as the GIA, AGL or Gubelin of origin adds to value. Gemstone color can be described in terms of hue and tone.
Hue is understood as the "color" of the gemstone. Saturation refers to the vividness or brightness of the hue, tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary and secondary hues, various tonal levels and at various levels of saturation. Blue sapphires are evaluated based upon the purity of their primary hue. Purple and green are the most common secondary hues found in blue sapphires. Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are said to be of fine quality. Gray is the normal saturation mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, therefore has a distinctly negative effect; the color of fine blue sapphires may be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15%, without the least admixture of a green secondary hue or a gray mask.
The 423-carat Logan sapphire in the National Museum of Natural History, in Washington, D. C. is one of the largest faceted gem-quality blue sapphires in existence. Sapphires in colors other than blue are called "fancy" or "parti colored" sapphires. Fancy sapphires are found in yellow, green, brown and violet hues. Particolored sapphires are those stones. Australia is the largest source of particolored sapphires. Particolored sapphires cannot be created synthetically and only occur naturally. Colorless sapphires have been used as diamond substitutes in jewelry. Pink sapphires occur in shades from light to dark pink, deepen in color as the quantity of chromium increases; the deeper the pink color, the higher their monetary value. In the United States, a minimum color saturation must be met to be called a ruby, otherwise the stone is referred to as a pink sapphire. Padparadscha is a delicate, light to medium toned, pink-orange to orange-pink hued corundum found in Sri Lanka, but found in deposits in Vietnam and parts of East Africa.
Padparadscha sapphires are rare. The name is derived from a color akin to the lotus flower. Natural padparadscha sapphires draw higher prices than many of the finest blue sapphires. More sapphires of this color have appeared on the market as a result of a new artificial treatment method called "lattice diffusion". A star sapphire is a type of sapphire. Star sapphires contain intersecting needle-like inclusions following the underlying crystal structure that causes the appearance of a six-rayed "star"-shaped pattern when viewed with a single overhead light source; the inclusion is the mineral rutile, a mineral composed of titanium dioxide. The stones are cut en cabochon with the center of the star near the top of the dome. Twelve-rayed stars are found because two different sets of inclusions are found within the
A regular dodecahedron or pentagonal dodecahedron is a dodecahedron, regular, composed of twelve regular pentagonal faces, three meeting at each vertex. It is one of the five Platonic solids, it has 12 faces, 20 vertices, 30 edges, 160 diagonals. It is represented by the Schläfli symbol. If the edge length of a regular dodecahedron is a, the radius of a circumscribed sphere is r u = a 3 4 ≈ 1.401 258 538 ⋅ a OEIS: A179296and the radius of an inscribed sphere is r i = a 1 2 5 2 + 11 10 5 ≈ 1.113 516 364 ⋅ a while the midradius, which touches the middle of each edge, is r m = a 1 4 ≈ 1.309 016 994 ⋅ a These quantities may be expressed as r u = a 3 2 ϕ r i = a ϕ 2 2 3 − ϕ r m = a ϕ 2 2 where ϕ is the golden ratio. Note that, given a regular dodecahedron of edge length one, ru is the radius of a circumscribing sphere about a cube of edge length ϕ, ri is the apothem of a regular pentagon of edge length ϕ; the surface area A and the volume V of a regular dodecahedron of edge length a are: A = 3 25 + 10 5 a 2 ≈ 20.645 728 807 a 2 V = 1 4 a 3 ≈ 7.663 118 9606 a 3 Additionally, the surface area and volume of a regular dodecahedron are related to the golden ratio.
A dodecahedron with an edge length of one unit has the properties: A = 15 φ 3 − φ V = 5 φ 3 6 − 2 φ The regular dodecahedron has two special orthogonal projections, centered, on vertices and pentagonal faces, correspond to the A2 and H2 Coxeter planes. In perspective projection, viewed on top of a pentagonal face, the regular dodecahedron can be seen as a linear-edged Schlegel diagram, or stereographic projection as a spherical polyhedron; these projections are used in showing the four-dimensional 120-cell, a regular 4-dimensional polytope, constructed from 120 dodecahedra, projecting it down to 3-dimensions. The regular dodecahedron can be represented as a spherical tiling; the following Cartesian coordinates define the 20 vertices of a regular dodecahedron centered at the origin and suitably scaled and oriented: where ϕ = 1 + √5/2 is the golden ratio ≈ 1.618. The edge length is 2/ϕ = √5 − 1; the circumradius is √3. Similar to the symmetry of the vertex coordinates, the equations of the twelve facets of the regular dodecahedron display symmetry in their coefficients: x ± ϕy = ±ϕ2 y ± ϕz = ±ϕ2 z ± ϕx = ±ϕ2 The dihedral angle of a regular dodecahedron is 2 arctan or 116.56505117707798935157219372045°.
OEIS: A137218 Note that the tangent of the dihedral angle is −2. If the original regular dodecahedron has edge length 1, its dual icosahedron has edge length ϕ. If the five Platonic solids are built with same volume, the regular dodecahedron has the shortest edges, it has 43,380 nets. The map-coloring number of a regular dodecahedron's faces is 4; the distance between the vertices on the same face not connected by an edge is ϕ times the edge length. If two edges share a common vertex the midpoints of those edges form a 36-72-72 triangle with the body center; the regular dodecahedron is the third in an infinite set of truncated trapezohedra which can be constructed by truncating the two axial vertices of a pentagonal trapezohedron. The stellations of the regular dodecahedron make up three of the four Kepler–Poinsot polyhedra. A rectified regular dodecahedron forms an
Rutile is a mineral composed of titanium dioxide. Rutile is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known including anatase, brookite. Rutile has one of the highest refractive indices at visible wavelengths of any known crystal and exhibits a large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of certain optical elements polarization optics, for longer visible and infrared wavelengths up to about 4.5 μm. Natural rutile may contain up to significant amounts of niobium and tantalum. Rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light. Rutile was first described in 1803 by Abraham Gottlob Werner. Rutile is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks. Thermodynamically, rutile is the most stable polymorph of TiO2 at all temperatures, exhibiting lower total free energy than metastable phases of anatase or brookite.
The transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three main polymorphs, it is the primary titanium bearing phase in most high-pressure metamorphic rocks, chiefly eclogites. Within the igneous environment, rutile is a common accessory mineral in plutonic igneous rocks, though it is found in extrusive igneous rocks those such as kimberlites and lamproites that have deep mantle sources. Anatase and brookite are found in the igneous environment as products of autogenic alteration during the cooling of plutonic rocks; the occurrence of large specimen crystals is most common in pegmatites and granite greisens. Rutile is found as an accessory mineral in some altered igneous rocks, in certain gneisses and schists. In groups of acicular crystals it is seen penetrating quartz as in the fléches d'amour from Graubünden, Switzerland. In 2005 the Republic of Sierra Leone in West Africa had a production capacity of 23% of the world's annual rutile supply, which rose to 30% in 2008.
Rutile has a tetragonal unit cell, with unit cell parameters a = b = 4.584 Å, c = 2.953 Å. The titanium cations have a coordination number of 6, meaning they are surrounded by an octahedron of 6 oxygen atoms; the oxygen anions have a coordination number of 3. Rutile shows a screw axis when its octahedra are viewed sequentially. Rutile crystals are most observed to exhibit a prismatic or acicular growth habit with preferential orientation along their c axis, the direction; this growth habit is favored as the facets of rutile exhibit the lowest surface free energy and are therefore thermodynamically most stable. The c-axis oriented growth of rutile appears in nanorods and abnormal grain growth phenomena of this phase. In large enough quantities in beach sands, rutile forms an important constituent of heavy minerals and ore deposits. Miners extract and separate the valuable minerals – e.g. rutile and ilmenite. The main uses for rutile are the manufacture of refractory ceramic, as a pigment, for the production of titanium metal.
Finely powdered rutile is a brilliant white pigment and is used in paints, paper and other applications that call for a bright white color. Titanium dioxide pigment is the single greatest use of titanium worldwide. Nanoscale particles of rutile are transparent to visible light but are effective in the absorption of ultraviolet radiation; the UV absorption of nano-sized rutile particles is blue-shifted compared to bulk rutile, so that higher-energy UV light is absorbed by the nanoparticles. Hence, they are used in sunscreens to protect against UV-induced skin damage. Small rutile needles present in gems are responsible for an optical phenomenon known as asterism. Asteriated gems are known as "star" gems. Star sapphires, star rubies, other "star" gems are sought after and are more valuable than their normal counterparts. Rutile is used as a welding electrode covering, it is used as a part of the ZTR index, which classifies weathered sediments. Rutile, as a large band-gap semiconductor, has in recent decades been the subject of significant research towards applications as a functional oxide for applications in photocatalysis and dilute magnetism.
Research efforts utilize small quantities of synthetic rutile rather than mineral-deposit derived materials. Synthetic rutile is sold under a variety of names, it can be produced from the titanium ore ilmenite through the Becher process. Pure synthetic rutile is transparent and colorless, being yellow, in large pieces. Synthetic rutile can be made in a variety of colors by doping; the high refractive index gives an adamantine luster and strong refraction that leads to a diamond-like appearance. The near-colorless diamond substitute is sold as "Titania", the old-fashioned chemical name for this oxide. However, rutile is used in jewellery because it is not hard, measuring only about 6 on the Mohs hardness scale; as the result of growing research interest in the photocatalytic activity of titanium dioxide, in both anatase and rutile phases, rutile TiO2 in powder and thin film form is fabricated in laboratory conditions through solution based routes using inorgainc precursors or organometallic precursors (typically alkoxides such as titanium isopropoxide known as
The mineral pyrite, or iron pyrite known as fool's gold, is an iron sulfide with the chemical formula FeS2. Pyrite is considered the most common of the sulfide minerals. Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold; the color has led to the nicknames brass and Brazil used to refer to pyrite found in coal. The name pyrite is derived from the Greek πυρίτης, "of fire" or "in fire", in turn from πύρ, "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel. By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulfide minerals. Pyrite is found associated with other sulfides or oxides in quartz veins, sedimentary rock, metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has been identified in the sclerites of scaly-foot gastropods. 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% gold by weight. Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun. Pyrite has been used since classical times to manufacture copperas. Iron pyrite was allowed to weather; the acidic runoff from the heap was boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of sulfuric acid. By the 19th century, it had become the dominant method. Pyrite remains in commercial use for the production of sulfur dioxide, for use in such applications as the paper industry, in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS and elemental sulfur starts at 540 °C. A newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium batteries.
Pyrite is a semiconductor material with a band gap of 0.95 eV. Pure pyrite is n-type, in both crystal and thin-film forms due to sulfur vacancies in the pyrite crystal structure acting as n-dopants. During the early years of the 20th century, pyrite was used as a mineral detector in radio receivers, is still used by crystal radio hobbyists; until the vacuum tube matured, the crystal detector was the most sensitive and dependable detector available – with considerable variation between mineral types and individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector. Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost photovoltaic solar panels. Synthetic iron sulfide was used with copper sulfide to create the photovoltaic material.. More recent efforts are working toward thin-film solar cells made of pyrite.
Pyrite is used to make marcasite jewelry. Marcasite jewelry, made from small faceted pieces of pyrite set in silver, was known since ancient times and was popular in the Victorian era. At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, not to the orthorhombic FeS2 mineral marcasite, lighter in color and chemically unstable, thus not suitable for jewelry making. Marcasite jewelry does not contain the mineral marcasite. China represents the main importing country with an import of around 376,000 tonnes, which resulted at 45% of total global imports. China is the fastest growing in terms of the unroasted iron pyrites imports, with a CAGR of +27.8% from 2007 to 2016. In value terms, China constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is best described as Fe2+S22−.
This formalism recognizes. These persulfide units can be viewed as derived from hydrogen disulfide, H2S2, thus pyrite would be more descriptively, not iron disulfide. In contrast, molybdenite, MoS2, features isolated sulfide centers and the oxidation state of molybdenum is Mo4+; the mineral arsenopyrite has the formula FeAsS. Whereas pyrite has S2 subunits, arsenopyrite has units, formally derived from deprotonation of H2AsSH. Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+3−. Iron-pyrite FeS2 represents the prototype compound of the crystallographic pyrite structure; the structure is simple cubic and was among the first crystal structures solved by X-ray diffraction. It belongs to the crystallographic space group Pa3 and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant a of stoichiometric iron pyrite FeS2 amounts to 541.87 pm. The unit cell is composed of a Fe face-centered cubic sublattice into.
The pyrite structure is used by other compounds MX2 of trans
Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO32. This opaque, green banded mineral crystallizes in the monoclinic crystal system, most 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 do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals occur; the stone's name derives from Greek Μολοχίτης λίθος molochitis lithos, "mallow-green stone", from μολόχη molōchē, variant of μαλάχη malāchē, "mallow". The mineral was given this name due to its resemblance to the leaves of the mallow plant. Malachite was extensively mined at the Great Orme mines in Britain 3,800 years ago using stone and bone tools. Archaeological evidence indicates that mining activity ended around 600 B. C. E with up to 1,760 tonnes of copper being produced from the mined Malachite. Archaeological evidence indicates that the mineral has been mined and smelted to obtain copper at Timna Valley in Israel for over 3,000 years.
Since malachite has been used as both an ornamental stone and as a gemstone. In ancient Egypt the colour green was associated with death and the power of resurrection as well as new life and fertility. Ancient Egyptians believed that the afterlife contained an eternal paradise which resembled their lives but with no pain or suffering, referred to this place as the ‘Field of Malachite’. Malachite was used as a mineral pigment in green paints from antiquity until about 1800; the pigment is moderately lightfast sensitive to acids, varying in color. This natural form of green pigment has been replaced by its synthetic form, among other synthetic greens. Malachite is used for decorative purposes, such as in the Malachite Room in the Hermitage Museum, which features a huge malachite vase, the Malachite Room in Castillo de Chapultepec in Mexico City. "The Tazza", a large malachite vase, one of the largest pieces of malachite in North America and a gift from Tsar Nicholas II, stands as the focal point in the centre of the room of Linda Hall Library.
Malachite has been used on the base of the FIFA World Cup Trophy. A 17th-century Spanish superstition held that having a child wear a lozenge of malachite would help them sleep, keep evil spirits at bay. Malachite results from the weathering of copper ores, is found together with azurite and calcite. Except for its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. Malachite is more common than azurite and is associated with copper deposits around limestones, the source of the carbonate. Large quantities of malachite have been mined in Russia. Ural malachite is not being mined at present, but G. N Vertushkova reports the possible discovery of new deposits of malachite in the Urals, it is found worldwide including in the Democratic Republic of the Congo. Basic copper carbonate Aventurine Brochantite Chrysocolla Dioptase Plancheite List of inorganic pigments Hurlbut, Cornelius S.. Virtual tour of the Malachite Room Malachite, Colourlex The dictionary definition of malachite at Wiktionary Media related to Malachite at Wikimedia Commons
A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire and diamond; the word ruby comes from Latin for red. The color of a ruby is due to the element chromium; some gemstones that are popularly or called rubies, such as the Black Prince's Ruby in the British Imperial State Crown, are spinels. These were once known as "Balas rubies"; the quality of a ruby is determined by its color and clarity, along with carat weight, affect its value. The brightest and most valuable shade of red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. Ruby is the traditional birthstone for July and is pinker than garnet, although some rhodolite garnets have a similar pinkish hue to most rubies.
The world's most valuable ruby is the Sunrise Ruby. Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0 and moissanite falling somewhere in between corundum and diamond in hardness. Sapphire and pure corundum are α-alumina, the most stable form of Al2O3, in which 3 electrons leave each aluminum ion to join the regular octahedral group of six nearby O2− ions; when a chromium atom replaces an occasional aluminum atom, it too loses 3 electrons to become a chromium3+ ion to maintain the charge balance of the Al2O3 crystal. However, the Cr3 + ions have electron orbitals in different directions than aluminum; the octahedral arrangement of the O2− ions is distorted, the energy levels of the different orbitals of those Cr3+ ions are altered because of the directions to the O2− ions. Those energy differences correspond to absorption in the ultraviolet and yellow-green regions of the spectrum.
If one percent of the aluminum ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission of 694-nanometer-wavelength red light, which adds to its red color and perceived luster. After absorbing short-wavelength light, there is a short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs. If 694-nanometer photons pass through the crystal during that time, they can stimulate more fluorescent photons to be emitted in-phase with them, thus strengthening the intensity of that red light. By arranging mirrors or other means to pass emitted light through the crystal, a ruby laser in this way produces a high intensity of coherent red light. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes.
The rough stone is heated before cutting. These days all rubies are treated in some form, with heat treatment being the most common practice. Untreated rubies of high quality command a large premium; some rubies show a three-point or six-point asterism or "star". These rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a single-light source and move across the stone as the light moves or the stone is rotated; such effects occur. This is one example. Furthermore, rubies can show color changes—though this occurs rarely—as well as chatoyancy or the "cat's eye" effect. Gemstone-quality corundum in all shades of red, including pink, are called rubies. However, in the United States, a minimum color saturation must be met to be called a ruby. Drawing a distinction between rubies and pink sapphires is new, having arisen sometime in the 20th century; the distinction between ruby and pink sapphire is not clear and can be debated. As a result of the difficulty and subjectiveness of such distinctions, trade organizations such as the International Colored Gemstone Association have adopted the broader definition for ruby which encompasses its lighter shades, including pink.
The Mogok Valley in Upper Myanmar was for centuries the world's main source for rubies. That region has produced some exceptional rubies, however in recent years few good rubies have been found. In central Myanmar, the area of Mong Hsu began producing rubies during the 1990s and became the world's main ruby mining area; the most found ruby deposit in Myanmar is in Namya located in the northern state of Kachin. Rubies have been mined in Thailand, in the Pailin and Samlout District of Cambodia, as well as in Afghanistan, Brazil, India, Namibia and Scotland. In Sri Lanka, lighter shades of rubies are more found; the Republic of Macedonia is the only country in mainland Europe to have occurring rubies. They can be found around the city of
Selenite known as satin spar, desert rose, or gypsum flower are four crystal structure varieties of the mineral gypsum. These four varieties of gypsum may be called selenite. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium, the similarity of the names of the substances coming from the Ancient Greek word for the Moon; some of the largest crystals found are of selenite, the largest specimen found in the Naica Mine's Cave of the Crystals being 12 metres long and weighing 55 tons. The etymology of selenite is through Middle English selenite, from Latin selenites, from Greek selēnitēs moonstone or stone of the moon, from selēnē; the ancients had a belief that certain transparent crystals waned with the moon. From the 15th century, "selenite" has referred to the variety of gypsum that occurs in transparent crystals or crystalline masses. All varieties of gypsum are soft minerals.
This is the most important identifying characteristic of gypsum, as any variety of gypsum can be scratched with a fingernail. Because gypsum has natural thermal insulating properties, all varieties feel warm to the touch. Though sometimes grouped together as "selenite", the four crystalline varieties have differences. General identifying descriptions of the related crystalline varieties are: most transparent and colorless: it is named after Greek σεληνη "the moon". If selenite crystals show translucency, and/or color, it is caused by the presence of other minerals, sometimes in druse druse is the crust of tiny, minute, or micro crystals that form or fuse either within or upon the surface of a rock vug, geode, or another crystal most silky and translucent. Rosette shaped gypsum with outer druse of sand or with sand throughout – most sand colored the desert rose name can be applied to barite desert roses – barite is a harder mineral with higher density rosette shaped gypsum with spreading fibers – can include outer druse the difference between desert roses and gypsum flowers is that desert roses look like roses, whereas gypsum flowers form a myriad of shapes Varieties of gypsum known as "satin spar" and "alabaster" are used for a variety of ornamental purposes like sculptures and a substitute for window glass.
But because of the long history of the commercial value and use of both gypsum and alabaster, the four crystalline varieties have been somewhat ignored, except as a curiosity or as rock collectibles. Crystal habit refers to the shapes. Selenite crystals occur as tabular and columnar crystals with no imperfections or inclusions, thereby can appear water or glass-like. Many collectible selenite crystals have interesting inclusions such as, accompanying related minerals, interior druse and fossils. In some rare instances, water was encased as a fluid inclusion. Selenite crystals sometimes form in thin tabular or mica-like sheets and have been used as glass panes as at Santa Sabina in Rome. Selenite crystals sometimes will exhibit bladed rosette habit with accompanying transparent, columnar crystals. Selenite crystals can be found both attached to a matrix or base rock, but can be found as entire free-floating crystals in clay beds. Satin spar is always prismatic and fibrous in a parallel crystal habit.
Satin spar occurs in seams, some of them quite long, is attached to a matrix or base rock. Desert roses are most bladed, exhibiting the familiar shape of a rose, always have an exterior druse. Desert roses are always unattached to a matrix or base rock. Gypsum flowers are most acicular, scaly and lenticular. Gypsum flowers most exhibit simple twinning. Selenite crystals can exhibit “arrow/spear-head” as well as “duck-bill” twins. Both selenite crystals and gypsum flowers sometimes form quite densely in acicular nets. Gypsum flowers are attached to a matrix or base rock. Gypsum crystals are colorless, gray, beige, pink, light red, green. Colors are caused by the presence of other mineral inclusions such as, copper ores and sulfides, iron ores, calcite and opal. Gypsum crystals can be transparent and opaque. Opacity can be caused by impurities, inclusions and crust, can occur in all four crystalline varieties. Both selenite and satin spar are glassy or vitreous and silky – on cleavage surfaces. Luster is not exhibited in the rosettes, due to their exterior druse.
Gypsum flowers exhibit more luster than desert r