Before we go further, it is a good idea to define gemstones, since the them does not always refer to a mineral, Originally, most raw materials used for gems came from the rocks and minerals in the earth’s crust, but in the few favored places in the world, primitive man discovered beautiful pearls within oysters and, in certain sedimentary formations, amber and jet; and because of their beauty and value, they too were classed as gemstones. Later, such materials as tortoise shell, pearl shell, coral, and number of types of ivory were added to the list, and most modern books on gemology, these are described and discussed along with mineral gemstones.
MINERAL GEMSTONES.
About 150 years ago, Arthur Aikin, Secretary to he Gemological Society of Great Britain, wrote a small mineralogy in which he listed about 250 minerals that were well recognized at the time. By the close of the nineteenth century, the list had grown to about 750 species; today it is over 2000. Despite the rapid rise in the number of minerals recognized as separate species, there are still only about a hundred that provide gems from suitable pieces of rough, of these, only about twenty-five are known to the layman. The mineral species furnishing the principal gemstones of greatest value, or the classical precious stones, are:
Diamond
Corundum (ruby and sapphire)
Beryl (emerald, aquamarine, etc...)
Chysoberyl (alexandrite, catseye, etc...)
Opal (white and black)
the following species furnish important gemstones, or those regulary handled in the gem and jewelry trade:
Feldspar Group (moonstones, amazonite, etc...)
Garnet Group
Jadeite
Nephrite
Olivine (periodot)
Quartz (amethyst, citrine, chalcedony, etc...)
SPinel
Topaz
Tourmaline
Turquois
Zircon
At this point it is wise to distinguish between certain gemstones that are composed of several minerals and, hence, are more like rocks, geologically speaking, that single mineral species. Prominent among such are marbles, which though usually composed of a single species, in this instance, calcite, occur in such quantity that they are classed as rocks rather than as large masses of a single mineral. Other rocklike gemstones are serpentine, lapis lazuli, various granites, and other stones that may or may not de good enough to use in jewelry but are frequently carved or cut into ornamental objects, often of large size. The following list of gemstones of lesser importance includes both mineral species and rock types:
calcite
gypsum
idocrase
lapis lazuli
odsidian
serpentine
steatite
The following gemstones are so rare, or for some reason unsutide for use in jewerly, that they are seldom seen outside collections:
Amblygoinite Cassiterite
Anatase Danburite
Andalisite Datolite
Apetite Diopside
Apophyllite Dioptase
Axinite Enstatite
Azurite Epidote
Benitolte Euclase
Beryllonite Hambergite
Brazilianite Hemimorphite
Brookite IoliteTHE QUALITIES OF GEMSTONES
What qualities distinguish gemstones from ordinary rocks and minerals? Why are certain of them prized and others scorned? There is no doubt that the most important quality is a beauty, for without it a mineral or rock will not be prized, regardless of what else it has. Gemstones are therefore attractive to eye, primarily because of vivid coloration, often enhanced by clever cutting , but also because of intriguing patterns, inclusions, or some other characteristic that lift them above the ordinary. Beauty is evident in the strong coloration of red ruby, blue sapphire, and green emerald, bud it spangles of aventurine, and the gleaming coppery needles of rutilated quartz. Since gems are meant to be worn, they are liable to be rubbed, chipped, or knocked against hard objects. It is important that resist this treatment, or be durable. The importance of this quality soon proves itself in gems set in rings or bracelets. Those that are strong and hard, like diamond, ruby, sapphire and chrysoberyl, will sparkle and gleam whit undiminished luster after years of wear have eroded the gold or platinum of the settings to the point where stones may be lost unless the settings are repaired. On the other hand, durability in not all important.
Consider opal as an example. this gemstones is brittle and soft, when worn rings, soon develops a frosted surface feom rubbing and knocking unless its wearer is extremely careful. Obviusly it is not nearly as durable as diamond and sapphire, but is beauty is so overwhelmingly great that is softness is tolerated. However, as a general rule, principal and important gemstones are noted for the fact that they are harder and tougher that many other minerals that may be considered as candidates for gemstones rank.
Because of the great rise in amateur gen cutting in the lasr few decades, many minerals that do not qualify as genuine gemstones because they lack durability are nevertheless cut as curiosoties and others are cut because they are so soft or fragile thet the difficulities, like an unscaled mountain to a mountain climber, present a challenge which cannot be ignored. Many such ''gemstones'' are listed in chapter 19, and are included not to swell the list of classical gemstones, but because thy offter a strong challenge to the cutter who is intereseted in goign beyond mastery of ordinary kinds.
The last important quality of most gemstones is that of rarity. This is not really a quality of gemstones but rather the way people who are interested in gems think of them. It is human nature to prize the rare, and no amount of reasoning will nullify the fact that between two objects of equall beauty, it is likely that the rarer one will be prized more highly.
TRADUCCION AL ESPAÑOL:
Piedras preciosas La materia prima para la talla
Nadie sabe cuánto tiempo atrás el hombre desarrollo el amor por las gemas.
Cada civilización desenterrada por los arqueólogos mostraron que sus miembros apreciaban cierto valor por los minerales coloridos para adornos personales algunas ocasiones, como en el caso de el jade de la china, que se mantuvo como sagrado.
El tallador de piedras disfruto de privilegios especiales, porque solamente él conocía los secretos de las piedras confiadas a su cuidado y, aparentemente mágicas, podía darles forma, a pesar del hecho que eran supremamente más duras que los finos metales.
Los antiguos griegos, y después de ellos los latinos, nos dieron el nombre de talladores del latín lápiz como el nombre de los artesanos quienes grababan piedras o gemas preciosas.
Por cientos de años el arte de la talla estuvo reservado a unos pocos y sólo en las últimos décadas se ha vuelto conocido, hasta el punto donde cualquiera puede aprender a modificar materia prima (piedras preciosas) a gemas, esculturas y muchos otros objetos de ornamento.
Antes de ir a lo más remoto, es buena idea definir Piedra-Preciosa, es claro que el término no siempre se refiere a un mineral.
Originalmente, la mayoría de la materia prima se usaba para gemas provenientes de las rocas y minerales en la corteza terrestre, pero en algunos lugares favorecidos en el mundo, el hombre primitivo descubrió hermosas perlas en las ostras y, en ciertas formaciones sedimentarias, ámbar y azabache, y debido a su hermosura y valor, ellos también se clasificaron como piedras preciosas.
Después tales materiales como el carey, la perla, el coral, y un numero de tipos de marfil se añadian a la lista, y en mas libros modernos en gemologia, estos se describen y discuten junto con el mineral piedras preciosas.
Minerales Piedras Preciosas
Cerca de 150 años atrás, Artur Aikin, Secretario de la Sociedad Geológica de Gran Bretaña, escribió una pequeña lista de minerales en el cual incluyo cerca de 250 minerales que fueron bien reconocidos con el tiempo.
Cerca del siglo diecinueve, la lista se agrando con cerca de 750 especies, hoy día hay por encima de 2000.
A pesar del rápido ascenso en el número de minerales reconocidos como diferentes especies, hay aun cerca de 100 son las únicas que proveen piezas de rugosidad adecuada, de estos solamente 25 son conocidos por el hombre común.
Las especies minerales suministran las principales piedras preciosas de gran valor, o las clásicas piedras preciosas, son las siguientes:
Diamante, corindón (rubí y zafiro), berilo (esmeralda, aguamarina,, etc), cresoberilo (alejandrita, ojo de gato, etc), ópalo (blanco y negro)
Las siguientes especies proporcionan importantes piedras preciosas, o de lo que habitualmente se maneja en el comercio de piedras preciosas y joyería:
Grupo de feldespato (piedra luna, amazonita, etc), Grupo granate jadeita, nephrite, olivino (peridoto), cuarzo (amatista, citrino, calcedonia, etc), espinela, topacio, turmalina, turquesa, circón.
En este punto es conveniente distinguir entre ciertas piedras preciosas que se componen de varios minerales y, por lo tanto, se parecen más a las rocas, geológicamente hablando, que la única especie mineral sencilla.
Entre esas son mármoles, que aunque por lo general se componen de una sola especie, en este caso, calcita, se produce en tal cantidad que son clasificadas como rocas, más que como grandes masas de un solo mineral.
Otras rocas piedras preciosas son serpentina, lapiz lazuli, varios granitos, piedras y otros que pueden o no ser lo suficientemente buenas para el uso en la joyería, pero a menudo de gran son talladas o cortadas para objetos ornamentales, a menudo de gran tamaño.
La siguiente lista de piedras preciosas de menor importancia incluye tanto especies minerales y tipos de roca:
Calcita, fluorita, yeso, hermatite, idocrase, lapislázuli, malaquita, obsidiana, pirita, rhodonite, scapolite, serpentina, sinhalite, smithsonite, sodalita, spodumene, esteatita, thomsonite, variscite, zoisite.
Las siguientes piedras preciosas son tan raras, o por alguna razón no aptas para su uso en joyería, que son pocas veces vistos fuera de las colecciones:
Amblygonite, anatasa, andalusite, apatita, apophyllite, axinite, azurita, benitoite, beryllonite, brazilianite, brookite, casiterita, danburite, datolite, diópsido, enstatite, epidota, euclase, hambergite, hemimorphite, iolite.
La talla y el pulido de las gemas son operaciones que tienen por objeto resaltar al máximo sus cualidades de color, brillo, transparencia, dispersión y resplandores, aún a costa de perder material y, en consecuencia, peso. 
Proporciones en la talla brillante.
