Albite (Plagioclase)Albite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one end member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. The intermediary members are Oligoclase, Andesine,Labradorite, and Bytownite. Oligoclase and Andesine are considered by some to be a variety of Albite rather then a separate mineral. The acclaimed Dana's System of Mineralogy lists these intermediary members as individual minerals, whereas the IMA does not recognize them as individual mineral species.
Albite also forms a series with Sanidine, and the intermediary member of this series isAnorthoclase. Albite can contain up to ten percent potassium replacing the sodium. If more than ten percent replaces the sodium, the mineral is no longer Albite, but Anorthoclase. Albite is a very common mineral, and is an important rock-forming mineral. It takes a longer time for Albite to crystallize than the other feldspars. This enables Albite to form in large and well crystallized examples. Albite is also a common accessory mineral to many rare and unusual minerals. The iridescent variety Peristerite sometimes exhibits an adularescent sheen. This produces an unusual form of Moonstone. Albite sometimes forms in association with the feldspar mineral Microcline in alternating patterns, and forms a feldspar rock known as Perthite. Amazonite (Microcline)Microcline is polymorphous with Orthoclase and Sanidine. These three minerals form thePotassium Feldspar group. They are almost identical in physical properties, and sometimes it is impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system. Crystals of Microcline are generally much larger than those of Orthoclase, and a deep green color is tell-tale sign of Microcline, since Orthoclase does not exist in a deep green color.
In some mineral reference guides, Microcline and Sanidine are wrongly categorized as variety of Orthoclase. Since it is so difficult to distinguish between Orthoclase, Sanidine, and Microcline, they may be simply called "Potassium Feldspar". Microcline sometimes forms in association with Albite or other Plagioclase feldspar in alternating patterns, and forms a feldspar rock known as Perthite. Feldspar (Orthoclase)Orthoclase is one of the most common minerals, and occurs in numerous mineral environments. It is polymorphous with the minerals Microcline and Sanidine. These three minerals form thePotassium Feldspar group. They are almost identical in physical properties, and it is sometimes impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system. Sanidine forms at high temperatures and has a disordered monoclinic symmetry, whereas Orthoclase forms at low temperatures and cools slowly, forming more ordered monoclinic crystals.
In some mineral reference guides, Microcline and Sanidine are wrongly categorized as variety of Orthoclase. Since it is so difficult to distinguish between Orthoclase, Sanidine, and Microcline, they may be simply called "Potassium Feldspar". OpalOpal is the most colorful of gems. Its splendid play of color is unsurpassed, and fine examples can even be more valuable than Diamond. The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. This phenomenon is often calledopalescence. The play of color may consist of large, individual flashes of color (known asschillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an Opal.
SodaliteSodalite is known for its often bright-blue color, and it usually contains white veins or streaking. Specimens are often polished or sliced into slabs for collectors. Sodalite is named in reference to its sodium ("soda") content.
The variety Hackmanite is sulfur-rich form of this mineral and is prized for its lovely pink or purple color and strong fluorescence. When in a rare crystallized form, this variety is especially aesthetic. Hackmanite has a unique optical property called tenebrescence, in which its color will be more saturated after exposure to ultraviolet light and then eventually fade. Agate QuartzAgate is the banded form of the mineral Chalcedony, which is a microcrystalline variety ofQuartz. Agate is the most varied and popular type of Chalcedony, having many varieties on its own. Although the pattern on every Agate is unique, the locality of an Agate will provide resemblances in banding style and color, thus lending many Agates with a geographic prefix. Some examples are Laguna Agate (named after Ojo Laguna, Mexico) or Botswana Agate (after the African country of Botswana). Other variety names used connote specific colors or patterns, such as Fire Agate or .
Agate usually forms in rounded nodules or knobs which need to be sliced open to bring out the internal pattern hidden in the stone. Most Agate is ugly in its natural state; specimens must bepolished to bring out their full beauty. Much of the Agate sold to collectors has been treated, in the form of tumbled stones or polished slabs. Popular collector forms of Agate include nodules or geodes sliced in the middle into two polished cross-sections, or thin slabs from nodule or geode cross-sections. The formation of Agate is most often from deposition of layers of silica filling voids in volcanicvesicles or other cavities. The layers form in stages with some of new layers providing an alternating color. Since the cavities are irregularly and uniquely shaped, each Agate forms its own pattern based on the original cavity shape. When a cavity is completely filled, it forms a solid mass of Agate, but often it is only partially filled, leaving a hollow void which often hascrystalline Quartz growths on its innermost layer. This is the cause of Agate forming the outer lining of most geodes. Agate is often dyed to enhance its colors. This is especially true of Agate from Brazil. Bright neon colors such as bright blue and red are rarely natural. Agate is named after the Achates River (now known as the Dirillo River) on the island of Sicily, Italy, whose upper waters were an ancient source of this gemstone. Amethyst QuartzAmethyst is a well known mineral and gemstone. It is the purple variety of the mineral Quartz, and its most valuable and prized variety. Its name derives from the Greek "amethystos", which means "not drunken", as Amethyst in antiquity was thought to ward off drunkenness. The color of some Amethyst specimens from certain localities slowly fade upon prolonged exposure to light. When used as a gemstone, Amethyst is often heat treated to deepen the color, or to transform it into Citrine. Some varieties may also change to a light green color, which is given the trade name "Prasiolite", or "Green Amethyst", as it is more commonly known in the gem trade.
Amethyst is most prevalent as small stubby pyramidal crystals, although several localities such as the Mexican occurrences are well-known for producing elegantly tall prismatic crystals, which are very highly regarded by collectors. Amethyst also forms the internal lining of geodes, some of which can be over 10 feet tall and weighing several tons. Onyx QuartzOnyx is a gemstone whose description can have several connotations. Its most accepted gemstone definition describes a solid black Chalcedony, or a banded or layered black and white Chalcedony. The term Onyx is occasionally used to described any engraved stone with a solid color base, or it may describe any banded gemstone with parallel banding. In its solid black form, Onyx is the most traditional black gemstone.
Citrine QuartzCitrine is the yellow to brownish-red variety of the mineral Quartz. It is a widely used as a gemstone, and after Amethyst it is the most popular Quartz gem. Most Citrine is formed byheat treating purple Amethyst. Citrine may also be produced by heat-treating Smoky Quartzfrom certain localities. In some Amethyst deposits, the Amethyst has been partially or fully changed over to yellow Citrine by natural means of heating.
Natural Citrine, which is rare, is yellow to orange-yellow, and occurs in much lighter hues than the heat-treated material, which is dark orange-brown to reddish-brown. Virtually all heat-treated material has a reddish tint, whereas the natural specimens do not. Natural light yellow Citrine is often called "Lemon Quartz" on the gemstone market. Sometimes Citrine has a "smoky" hue to it, and can be borderlined between Citrine and Smoky Quartz, with either definition being correct. http://www.minerals.net/mineral/citrine.aspx Chalcedony QuartzChalcedony is the form of Quartz that is compact and microcrystalline. It occurs in many different forms, colors, and patterns, and many varieties have been used as gemstones since antiquity. In the gemstone trade, the term Chalcedony is often used specifically to describe the white, gray, or blue translucent type of Chalcedony, but its technical term includes all additional varieties.
Crystal QuartzHas a Crystal structure, and is clear in color.
Jasper QuartzJasper is an opaque form of Chalcedony, which is a microcrystalline variety of the mineral Quartz. It often contains an abundance of impurities, and therefore some regard it as a rock instead of a mineral. Jasper is usually associated with brown, yellow, or reddish colors, but may be used to describe other opaque colors of Chalcedony such as dark or mottled green and orange. Some forms of Jasper are banded, and these banded Jaspers may appear similar to Agate, but unlike Agate they are opaque. When Jasper is dull and lacking interesting colors or patterns, it is not Jasper but rather Chert
.http://www.minerals.net/mineral/jasper.aspx Milky QuartzWhite, translucent to opaque variety of Quartz.
Rose QuartzRose Quartz is the rosy pink variety of Quartz. Its color is usually soft, ranging from very light pink to medium pink in intensity. It is often hazy or turbid, which makes it lack good transparency. Rose Quartz is fairly common and found in many places throughout the world, and can occur in very large examples in nature. This allows exceedingly large gemstones to be cut from it. The relative abundance of Rose Quartz, and its frequent lack of full transparency, diminish its importance as a pink gemstone in relation to other pink gemstones such as andTopaz, Tourmaline, and Kunzite
.http://www.minerals.net/gemstone/rose_quartz_gemstone.aspx |