Rutilated quartz

Rutilated quartz with very fine light colored rutile is called "angel hair."  Rutile derives its name from the Latinrutilus, meaning "red," in reference to the deep red color observed in some specimens when viewed by transmitted light. Although rutile is commonly reddish brown, it can also be yellowish, bluish, green or even violet.  Rutiles can be up to 10% iron.

golden threads but no silver needles... Rutilated quartz is a quartz with large inclusions of the mineral rutile, a titanium-rich material. Rutile forms in quartz as what appears to be glimmering gold and red threads or 'needles' arrayed in patterns inside the stone. Since every pattern of rutiles within the stone is unique, each piece of rutilated quartz is unique. carved rutilated quartz egg Until relatively recently, rutilated quartz was considered mainly an ornamental stone (fit for crystals and carving), but its unusual inclusions -- often seen as golden-colored (a phenomenon of refracted light) -- have made it an increasingly popular stone with jewelry designers and the public. Rutile itself is an interesting and important mineral. A significant source of titanium dioxide, the metal is used for high tech alloys because of its light weight, high strength and resistance to corrosion.

Bolivian beauty

The unusual color variation found inametrine is due to the presence of iron in different oxidation states within thecrystalline structure. Exactly how ametrine's bi-color comes about, geologically, is still not fully understood.  Ametrine is relatively inexpensive, given the fact there's only one commercial mine in the whole world. Although the it is the world's only ametrine mine, most of the Anahi mine's production is devoted to producing amethyst. To add some perspective on theinaccessibility of the mine: it takes 2 � hours to fly from Santa Cruz to the mine's landing strip -- or one can travel from Puerto Suarez (Bolivia) by boat up the Paraguay River to Lake Mandior�, a6 hour journey and then a 2 hour truck ride via a jungle trail.

bolivian beauty A bi-color stone -- and Bolivia's most spectacular export -- citrine makes up the yellow-orange part of ametrine and amethyst, the violet-purple part. Ametrine is formed when iron impurities in quartz are affected in different ways by heat. (An example of how this could happen is if one side of the crystal was facing a vent or other such heat source. Any change in pressure would affect the temperature forming the citrine and amethyst would begin to form instead.) the vast pantanal wetland of bolivia Located in the far eastern part of Bolivia, traditional land of the nomadic hunter-gatherer Ayoreo (pronounced "ai-o-reo"), the Anahi Mine is the major producer of high-quality ametrine in the world. The mine also produces anahite, as well as amethyst and citrine. In the midst of a nearly inaccessible rain forest zone -- near the famous Pantanal wetlands, an area that establishes the borderline between Bolivia and Brazil -- the mine is four hundred kilometers southeast of Santa Cruz and is reached primarily by bush plane. one anahi mine entrance photo: anahi mine Ametrine -- which initially appeared on the market as Bolivianite -- has only been available to consumers in any quantity since 1980 when the Anahi mine in Bolivia became operational. Before the discovery of the large deposit in Bolivia, ametrine was also known as amethyst-citrine quartz, trystine or golden amethyst.

Another name for common opal ispotch .

Another name for common opal ispotch . It's the orderliness of the silica spheres within the stone that separates precious opal from common opal.Precious opal is made up of tiny uniform spheres of transparent hard silica which fit together in an orderly three dimensional frame and sit in a "bath" of silica solution. But, incommon opal, the silica spheres are intoo much disarray to diffract light -- hence, no play-of-color. When there is color -- that is, bits with "play of color" mixed with potch, it'scalled -- duh -- "potch and color."

silica spheres of precious opal vs. potch Common opal is defined as lacking a "play of color" and includes a rather long list of stones, all of which lack opalescence, color or luster for the most part. "potch and color" Opaque or glassy in a wide range or colors, common opal can be sometimes have a waxy luster, and is often fluorescent. It may be colored or contain dendritic (moss-like) inclusions. There are many different common opals, including: Hyalite is a transparent, colorless-to-bluish opal which forms in cavities in volcanic rocks. Hydrophane is a porous, opaque, light-colored opal which becomes transparent when soaked in water. Lemon (yellow) opal often has green-gold tones, small black and red-orange streaks, and a waxy luster. Moss opal contains dendritic mineral inclusions, resembling ferns or moss. Peruvian opal comes in shades of turquoise, aqua, and pale blue. Pink opal is sometimes sold as pink silica and contains black inclusions and dendrites. Prase opal is bright green, due to the presence of nickel. Wood opal is a replacement of wood by non-precious opal, often retaining the grained appearance and bark texture.

Alluvial amethyst

alluvial amethyst Amethyst is dichroic, showing a bluish or reddish purple tinge when viewed from different angles. Much amethyst that is mined is heat-treated to change the color to yellow -- which explains much of the citrine on the market today, natural citrine being somewhat rare. amethyst mine, brazil photo:silvestre garimpo One of the world's major producers of natural amethyst is the Anahi Mine in Bolivia (which also produces ametrine). The mine is located in the midst of the rain forest zone near the Pantanal wetlands, which establishes the borderline between Bolivia and Brazil. Accessible primarily by bush plane, the mine is four hundred kilometers east and slightly south of Santa Cruz, Bolivia. In Brazil and Uruguay, amethyst is often found in alluvial deposits in the beds or former beds of rivers where miners use the techniques of placer mining. (Alluvial gems often have quite a high specific gravity [density] compared to other minerals so that they are easily trapped in depressions in stream beds. This causes them to become concentrated, making them easier to mine.)

Geodes are a variable phenomenonand, therefore, many theories exist toexplain how they are created. The term geode is derived from the Greek word geoides which means "earthlike."  Some geodes are completely filledwith small compact crystal formationssuch as agate, jasper or chalcedony and are called nodules. The only differencebetween a geode and a nodule is that a geode has a hollow cavity, and a nodule is solid.  Volcanic lavas such as basalts may have round or almond shaped gas holes, partially or completely filled withcalcite, chalcedony, agate, crystallized colorless or amethyst quartz or other minerals. Many easily accessible geode collecting sites exist in the western US -- including California, Arizona, Utah andNevada. The state of Iowa is also hasgeodes: in fact, they are so prevalent thegeode is Iowa's state rock. A relatively cheap stone because it is aquartz, amethyst is found throughout the world. Were amethyst not so plentiful it would be much more expensive, given its beautiful range of purple shades, ranging from deep purple to lilac to mauve to purplish reds. If, after creating citrine from amethyst, one decides amethyst would be more desirable, the pseudo-citrine can bechanged back to the original amethystcolor by subjecting it to X-ray radiation. Methods of accessing alluvial gem gravels include open pits, shafts and tunnels, and dredging.

geodes: the variable phenomenon One of the amethyst forms with which the public is most familiar is the geode, split into two halves. what is a geode? amethyst geode Geodes are hollow, crystal-lined globular rock cavities lined with crystals that are found in sedimentary rocks like limestone (calcium carbonate) and dolomite (calcium magnesium carbonate) or in volcanic rocks. how are geodes created?Beginning as bubbles in volcanic rock or as animal burrows, balls of mud or tree roots in sedimentary rock, over a period of millions of years the outer layers of silica cool and harden while at the same time water containing dissolved silica begins to seep into the lava cracks or cavities. Eventually, the deposited silica minerals create crystals, most of which point towards the center of the cavity. Each geode is unique -- its secrets can only be discovered by cracking it open or dissecting it with a rock saw. The size and formation of crystals and their different shades of color is what makes each geode special, as a geode's rough exterior gives no indication of the often breath-taking secrets held within. For those who collect geodes, the anticipation of finding out what's inside never fades.

Como se forma a cor dos diamantes?

Como se forma a cor dos diamantes?

Fonte: Jornal do ouro

a origem das cores naturais verde, violeta, alaranjada, branca, cinza e preta em diamantes. Verde Os diamantes de cor verde lapidados são muito raros e, geralmente, apresentam tons suaves com um componente modificador marrom, amarelo ou azul. Por outro lado, os espécimes brutos com um finíssimo recobrimento superficial verde, usualmente de óxido de cromo, são mais frequentes, inclusive no Brasil, onde são encontrados principalmente na região de Diamantina, em Minas Gerais. A cor verde interna em diamantes deve-se a diversas causas, sendo a mais importante delas a irradiação natural. Acredita-se que esta provenha de minerais radioativos presentes no kimberlito (rocha-matriz do diamante) próximo à superfície ou mesmo de águas radioativas que percolem o corpo kimberlítico. É o caso dos diamantes de boa parte do Tapajós. O mais famoso diamante verde conhecido é o Dresden, que se encontra atualmente em um museu na Alemanha, na cidade do mesmo nome. A gema apresenta forma de gota, pesa 41 ct e seu local de origem é objeto de intensa polêmica, sendo a Índia ou o Brasil a mais provável fonte. Há diamantes verdes tratados pelo menos desde a década de 40 e a maior parte dos vistos atualmente no mercado foram submetidos ao processo de altas pressões e temperaturas (HPHT), realizado em vários países, sobretudo nos EUA, Rússia e Suécia. Estas pedras têm coloração verde amarelada e são obtidos a partir de exemplares originalmente marrons, do tipo Ia. Embora determinadas propriedades gemológicas, tais como a elevada saturação da cor, a presença de graining e fraturas de tensão e a fluorescência verde amarelada gredosa sob UVC e UVL sugiram uma indução da cor pela mencionada técnica, a identificação irrefutável requer ensaios mais sofisticados, tais como espectroscopia de infravermelho e espectroscopia visível de baixa temperatura. Violeta Os diamantes violetas procedem quase exclusivamente da jazida de Argyle, na Austrália, e adicionalmente apresentam uma nuança acinzentada. Embora quase nada se saiba a respeito dos mecanismos que originem tal cor em escala atômica, há evidências de que esteja associada à presença do elemento hidrogênio. Alaranjada A cor alaranjada pura, sem qualquer componente modificador é, provavelmente, a mais rara dentre todas as cores em diamantes, até mais que a vermelha ou a verde. A origem desta cor segue sendo um mistério, embora se saiba que um centro desconhecido provoca o aparecimento de uma banda de absorção na região azul do espectro visível, centrada em 480 nanômetros (unidade de medida dos comprimentos das ondas luminosas, de abreviatura nm), o que dá lugar à cor complementar desta, a alaranjada. Branca Embora nas práticas comerciais seja comum referir-se equivocadamente a diamantes brancos quando se pretende descrever pedras aproximadamente incolores, esta cor de fato existe neste mineral. Acredita-se que os comprimentos de onda que compõem a luz branca são enviados por diminutas inclusões em todas as direções e em cada uma delas sejam recombinados para dar lugar à luz branca, conferindo ao diamante um aspecto leitoso ou opalescente. Cinza A cor cinza em diamantes é mais uma das quais a origem não está ainda esclarecida, embora hajam evidências de que esteja associada a defeitos relacionados à presença de hidrogênio. Em diamantes ricos neste elemento, a absorção da luz ocorre com igual intensidade em todos os comprimentos de onda do espectro visível, o que resulta em uma coloração acinzentada. Preta Os diamantes pretos, entre os quais o mais famoso representante é o russo Orlof, tornaram-se mais populares a partir dos anos 90 e devem sua cor à presença de uma grande quantidade de diminutas inclusões escuras, em forma de plaquetas, que se acredita serem majoritariamente do mineral grafita. Em alguns casos, estas inclusões são tão numerosas que dificultam o polimento do exemplar, o que influi, evidentemente, no aspecto final da gema. A cor preta - ou melhor, uma cor verde-azul que, por muitíssimo saturada, nos transmite a sensação de preta - também pode ser obtida artificialmente por tratamento, mediante intensa irradiação com nêutrons em diamantes facetados, sobretudo aqueles com graus de pureza muito baixos.

*Luiz Antônio Gomes da Silveira é gemólogo pós-graduado pela Universidade de Barcelona (1988), pela Associação Alemã de Gemologia (Deutschen Gemmologishen Gesellschaft) e pela Associação e Laboratório de Ensaios de Gemas da Grã-Bretanha (Gemmological Association and Gem Testing Laboratory of Great Britain). Engenheiro de Minas (UFMG/1985), é credenciado pela Secretaria da Receita Federal, Responsável Técnico pelo Gem Lab - Gemologia e Engenharia Mineral e ex-Instrutor de Cursos de Gemologia e Diamante na Ajomig/Sindijóias.