Minerals.net

Galena is the most common mineral containing lead, and has been well known throughout...  More

Galena is the most common mineral containing lead, and has been well-known throughout the centuries. It is often well crystallized and forms in many interesting and distinct crystal shapes. Some cubic crystals have their edges cut by the partial octahedral growth, some octahedral crystals have their points flattened by cubic growth, and many crystals are found somewhat in-between cubic and octahedral. Dodecahedral growths may partially be found in octahedral or cubic-octahedral crystals, resulting in bizarre and interesting shapes.

Galena is a primary mineral. Most of the lead minerals, such as Cerussite and Anglesite are secondary minerals formed from Galena. Impurities in the structure of Galena, such as silver and bismuth, may change Galena's cleavage properties. Galena containing bismuth may exhibit octahedral cleavage, and silver in Galena may cause a specimen to exhibit flaky, slightly bent cleavage fragments.

Galena specimens may tarnish when exposed to air, becoming dull in luster. Freshly cleaved specimens exhibit a strong metallic luster, but over time the luster turns more dull, although still metallic. The tarnish can be removed by scrubbing the specimen with water and mild soap.

Galena specimens must be taken care of more so then other minerals. They are easily damaged, and well formed crystals may shatter into small crystal fragments if put under slight pressure or dropped, so care should be taken when handling and transporting Galena specimens.
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The pictures below show just one example of each individually named common member of Garnet. For more images, see the specific pages on Almandine, Pyrope, Spessartine, Grossular, Andradite, and Uvarovite.

Garnet is not a single mineral, but a group contains closely related, isomorphous min...  More

Garnet is not a single mineral, but a group contains closely related, isomorphous minerals that form a series with each other. The Garnet members form intermediary minerals between each member, and may even intergrow within a single crystal. The Garnets vary only slightly in physical properties, and some of the members may be so similar that they are indistinguishable from one another without x-ray analysis.

The common Garnets can be divided into two subgroups:
Group 1: Garnets containing aluminum (Al) as their second element.
These include Pyrope, Almandine, and Spessartine. ("Pyralspite")

Group 2: Garnets containing calcium (Ca) as their first element.
These include Uvarovite, Grossular, and Andradite. ("Ugrandite")

The members of each group freely intermingle among one another. For example, the magnesium in Pyrope may be partially replaced by some iron from Almandine or by some manganese from Spessartine. However, between the two groups of Garnets, it is much rarer for them to intermingle.
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Gaspeite is a rare mineral, with a distinct yellowish apple green to bright green col...  More

Gaspeite is a rare mineral, with a distinct yellowish-apple-green to bright green color. It has recently become popular among both mineral and gemstone collectors. Gaspeite specimens may be polished or sliced into slabs when sold on the market. It usually has brownish veins of rock running through the mineral, which are pronounced in cut or polished specimens.

Gaspeite belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a solid solution series. All members of the calcite group crystallize in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction in transparent rhombohedrons.  Hide

Gibbsite is one of the three component minerals of the economically important aluminu...  More

Gibbsite is one of the three component minerals of the economically important aluminum ore Bauxite. Gibbsite was first discovered in 1820 by Chester Dewey (1784-1867) of Williams College, Massachusetts. It was first thought to be Wavellite, but a year later it was determined to be a separate mineral species and was subsequently named Hydrargillite. It was then renamed Gibbsite in 1822 by John Torrey (1796-1873) in honor of George Gibbs (1776-1833) of New Haven, a noted mineralogist whose important collection was acquired by Yale University.
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Many Glauberite specimens in collections are not truly Glauberite, but rather other m...  More

Many Glauberite specimens in collections are not truly Glauberite, but rather other minerals that formed a pseudomorph or epimorph over the Glauberite. Glauberite itself is in fact a rare and unstable mineral, but its remnants and castings are much more prevalent. This is evident by an abundance of empty casts and pseudomorphs found in localities where little or no Glauberite was ever found. There are some localities where hollow Glauberite crystal casts can be found in a rock or mineral base with the original Glauberite completely dissolved.

Glauberite forms in evaporite and clay deposits. These environments enable a crystal to grow without interference from attached matter, so crystals can be perfect on all sides. Such crystals are known as floater crystals.

Some Glauberite pseudomorphs from Camp Verde, Arizona, exhibit a deep green color. These are not natural and have been artificially dyed by certain dealers, thus the buyer should be aware.

True Glauberite does not keep well in collections for it is efflorescent, developing white powder on its surface which dulls its luster. To avoid this, specimens should be placed in conditions where this effect is minimal, such as a damp area. Pseudomorphs and epimorphs are stable and don't require extra protection from humidity.  Hide

Glaucophane is named from a combination of the Greek words i Glaukos, i meaning blue ...  More

Glaucophane is named from a combination of the Greek words Glaukos, meaning "blue", and Phainelein, meaning "appearance", alluding to its bluish color. Glaucophane forms a series with the less-common Ferro-glaucophane, where Glaucophane is the magnesium-rich end member and Ferro-glaucophane is the iron-rich end member.
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Since its original classification, Gmelinite was always regarded as a single mineral ...  More

Since its original classification, Gmelinite was always regarded as a single mineral species with a variable elemental makeup. In 1997, the Zeolite Subcommittee of the IMA divided this mineral into individual sub-species, thereby regarding Gmelinite as a series of three members. The series is defined by the presence of several variable elements in the following order: calcium, sodium, and potassium. Calcium-dominating Gmelinite is called Gmelinite-Ca, and is the most prevalent form of this series. Sodium-dominating Gmelinite, defined as Gmelinite-Na, and potassium-dominating Gmelinite, defined as Gmelinite-K, are both rare. Most Gmelinite specimens in collections are Gmelinite-Ca. A distinction among the different Gmelinite types is rarely made, and the members are generally just termed Gmelinite without further breakdown.

Gmelinite is very similar in structure and habit to the closely related Chabazite, though it can be distinguished by its more reflective luster and triangular crystal angles. Gmelinite often forms as a pseudomorph after Chabazite, retaining the original rhombic shape but forming modified faces.

Gmelinite was defined and named in 1825 by David Brewster in honor of Christian Gottlob Gmelin (1792-1860), a mineralogist and chemist at the University of Tübingen, Germany.  Hide

Goethite is a common mineral, and is a frequent matrix material for other more aesthe...  More

Goethite is a common mineral, and is a frequent matrix material for other more aesthetic minerals. It is usually a dark, uninteresting mineral, though specimens from a handful of locations (especially Colorado) are remarkable for their delicate and beautiful crystal growths and velvety botryoidal growths. Goethite is also frequent as black crystal sprays that form within geodes on drusy Quartz. It commonly forms a pseudomorph after other minerals, especially Marcasite, Pyrite, Siderite, and Gypsum.  Hide

Gold is one of the most popular and well known minerals, known for its value and spec...  More

Gold is one of the most popular and well-known minerals, known for its value and special properties since the earliest of time. Most of the natural Gold specimens that have been found since early times have been smelted for production. Nice specimens, therefore, are regarded very highly, and are worth much more than the standard gold value. Only recently have more specimens been available to collectors, as more miners have been saving some of the larger pieces for the collectors market.

Gold in its natural mineral form almost always has traces of silver, and may also contain traces of copper and iron. A Gold nugget is usually 70 to 95 percent gold, and the remainder mostly silver. The color of pure Gold is bright golden yellow, but the greater the silver content, the whiter its color is. Much of the gold mined is actually from gold ore rather then actual Gold specimens. The ore is often brown, iron-stained rock or massive white Quartz, and usually contains only minute traces of gold. To extract the gold, the ore is crushed, then the gold is separated from the ore by various methods.

Gold nuggets, a popular form of Gold with collectors, are formed when erosion causes a large piece of Gold to separate from its mother rock, and then gets carried into a stream or river. The flowing water tumbles the Gold, giving it its distinct rounded shape. The Gold eventually settles at the bottom of the water, and due to its heaviness remains there. Other nuggets also get caught in the same area, forming a placer deposit.

Gold is one of the heaviest minerals. When pure, it has a specific gravity of 19.3. Due to its weight, it can be panned because the Gold sinks to the bottom. In addition, it can be easily separated from other substances due to the weight differences. Gold is also the most malleable and ductile substance known. It can be flattened out to less than .00001 of an inch (less than .000065 cm), and a 1 oz. (28 gram) mass can stretch out to a distance of over 50 miles (75 kilometers). Gold is also one of the most resistant metals. It won't tarnish, discolor, crumble, or be affected by most solvents. This adds on to the uniqueness and allure of this mineral.

Gold is usually associated with Pyrite and other sulfides, and sometimes may not be noticed because of the association with these resembling minerals. In certain localities, minerals that contain these sulfides are heated high enough for the sulfides to dissolve, enabling the Gold to remain intact on the matrix. Such Gold is known as "Roasted Gold", and is occasionally sold to collectors.

For additional information, see the gemstone section on Gold.
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Goosecreekite is a rare and coveted member of the zeolite group . It is a relatively ...  More

Goosecreekite is a rare and coveted member of the zeolite group. It is a relatively new mineral, only being recognized by the IMA as a distinct mineral species in 1980. Goosecreekite is named after its type locality at the New Goose Creek Quarry in Leesburg, Virginia.
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Graphite is a mineral composed exclusively of the element carbon. Graphite has the sa...  More

Graphite is a mineral composed exclusively of the element carbon. Graphite has the same chemical composition as Diamond, which is also pure carbon, but the molecular structure of Graphite and Diamond is entirely different. This causes almost opposite characteristics in their physical properties.  Hide

div Greenockite is a rare mineral formed mostly of the element cadmium, and it is the...  More

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Grossular is member of the Garnet group, and is its most varicolored form, occurring ...  More

Grossular is member of the Garnet group, and is its most varicolored form, occurring in almost all colors except for blue. Grossular is often dark in color, but it also forms the lightest colored forms of Garnet, and can even be white or colorless. Although not as famous as Almandine and Pyrope, Grossular has some important gem varieties. These include the rare emerald-green Tsavorite and the orange to orange-brown Hessonite.

Grossular forms a solid solution series with Andradite, and can be virtually indistinguishable from it in localities where they both occur together. In some localities such as Mali, a distinction between these two Garnets is sometimes too complex, and a specimen may just be called "Andradite/Grossular since its full identification is lacking. Grossular is named for its color resemblance to gooseberries, which are scientifically known as ribes grossularium.  Hide

div Gummite nbsp is not a definitive mineral species, but rather an unspecific mixtur...  More

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Gypsum has many interesting properties, including its very unique crystal habits. Man...  More

Gypsum has many interesting properties, including its very unique crystal habits. Many Gypsum crystals are found perfectly intact without distortions or parts broken off. Such crystals are found in a clay beds as floater crystals, where they fully form without being attached to a matrix. Gypsum crystals are known for their flexibility, and slim crystals can be slightly bent. (Though trying to bend good crystals is not recommended, as their flexibility is weak, and if flexed too much they will break.)

Gypsum has the same chemical composition as the mineral Anhydrite, but contains water in its structure, which Anhydrite lacks. Many Anhydrite specimens absorb water, transforming into the more common Gypsum. Some Gypsum specimens show evidence of this, containing growths of crumpling layers that testify to their expansion from the addition of water.

In a small number of Gypsum specimens, water gets trapped inside a crystal in a hollow channel while the crystal forms. When such a crystal is rotated, a water "bubble" moves around inside it toward the lowest point in the channel. Such specimens are considered a mineralogical oddity, and are very desirable to collectors. These are called "enhydros".

Gypsum sometimes forms in sandy areas, and crystals may trap sand inside when forming, causing a specimen to become brown or gray and opaque. These sand inclusions sometimes form hourglass formations in a crystal. They are also present in the well-known "Desert Rose", which is rosette shaped Gypsum with sand inclusions. (The term "Desert Rose" also applies to rosette shaped Barite with sand inclusions, and the two should not be confused.)

Gypsum specimens should only be cleaned with water. Soaps and detergents should be avoided, as they can enter cracks and crevices of a crystal and ruin its luster.  Hide