October 2010 MIneral of the Month

Brazilian Agate

Brazilian agate is a variety of chalcedony and comprised of cryptocrystalline quartz. It has a hardness of 6.5 to 7.5 on the Mohs scale. It occurs in bands of varying color and transparency. The Brazilian varieties are characterized by peculiarities in the shape and color of the bands, which can be seen in sections when cut at right angles to the layers. The banding in Brazilian agates forms as silica from ground water is slowly deposited into cavities and veins in the older rock. Agate is found throughout the world as nodules in volcanic or other eruptive rock and also in hollow geode form. Brazil is a major producer of agates. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-eye, and are often found in association with opal. The colorful, banded rocks are used as a semiprecious gemstone. Brazilian agates can be artificially stained to produce a combination of colors more vivid than those found in the natural state. The agates from Brazil are mostly mined from decomposed volcanic ash and basalt from the late Permian age (248-275 million years ago) In Rio Grande do Sul the "agate mines" are normally just plowed fields in which loose agates are found and collected. Brazilian agates are very colorful stones with some of the most beautiful inclusion and structures imaginable. Agate is very hard and takes an excellent polish. Sadly, most of the market for Brazilian agates is for the dyed versions of these stones. When you see a pink,teal, purple or green agate it is dyed and not natural.

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September 2010 Mineral of the Month

Ocean Jasper

Ocean Jasper is a silicon dioxide mineral that occurs in highly silicified rhyolite. This means that it is in the Quartz family and just like all other Jaspers it has a hardness of 6.5 to 7. Ocean Jasper is sometimes called Orbicular Jasper, a broad term given to several Jaspers displaying perfect circles throughout the piece. The peculiar orbs or "bull's eye" patterns are caused when Quartz and feldspar crystallize in radial aggregates of needle shaped crystals. A few of these other Orbicular Jaspers are Poppy Jasper and Leopard Skin Jasper. Many of these other orbicular jaspers are found in various locations throughout the world; however none are as rare as Ocean Jasper! The vibrant colors visible in Ocean Jasper are caused by many different minerals. Red is caused by iron or hematite, light yellow or gray is caused by clay and brown or deep yellow is from goethite. Sometimes a dazzling display of sparkling tiny crystals occurs upon the surface. These little gems, known as druze, are the result of clear or white quartz formations. Many collectors seek specimens of Ocean Jasper with these unique crystals upon them. Another exceptional quality of Ocean Jasper is translucency. Many specimens are opaque and still very beautiful while others, when held in front of a strong light source, display what can only be described as another world! When viewed in front of a bright light the translucent or clear background illuminates and displays the contrasting solid orbs, which then reveal exactly why Ocean Jasper is sometimes called "Fish Eye Jasper". These solid spheres appear suspended in the illuminated quartz. Each piece of Ocean Jasper seems to have a mind of its own! For example, in some specimens a solid opaque background of mustard yellow contrasts with hundreds of tiny green circles. In others, a sparkling white surface displays diagonal lines of pink and red running in every direction. Almost every piece of Ocean Jasper displays at least one of the orbs, striking colors, crystal displays or translucency. The story of Ocean Jasper began many years ago. It was the early 1950's in Madagascar when a prospector brought Paul Obeniche of Madagascar Minerals Co. a sample of the curious new orbicular jasper. The prospector could not recall the source of the sample, however Paul estimated it may have been from the northwest coast of Madagascar. Reaching this particular location was extremely dangerous due to treacherous reefs, sheer rugged cliffs and no roads. The effort to find it was fruitless and this new Orbicular Jasper was soon forgotten. About 45 years later, photos of this unnamed Jasper reappeared in the Mineralogical Encyclopedia. This sparked everyone's curiosity and the Madagascar Mineral Company sent out several expeditions again. In 1999, after 45 days of visiting fishing villages along Madagascar's NW coast, the Orbicular Jasper was once again discovered! Luckily the expedition was sailing near Moravato, along the NW coast during low tide. As the strong ocean currents pushed back from the cliffs, the beautiful Orbicular Jasper was seen once again!

September 2010 Mineral of the MOnth

July 2010 Mineral of the Month

HOWLITE

Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a silicate mineral found in evaporate deposits. Howlite was discovered at Tick Canyon, California in 1868 by Henry How (1828-1879) He was a Canadian chemist, geologist, and mineralogist. In appearance, it is white with fine gray or black veins in an erratic, often web-like pattern, and is opaque with a sub-vitreous luster. Slabs of Howlite are often painted with scenes and designs that make artistic use of these veins. Its structure is monoclinic with a Mohs hardness of 3.5 and lacks regular cleavage. It is most often found in massive nodules that resemble a head of cauliflower and rarely in crystal form as tabular prisms.

Howlite is commonly used to make decorative objects such as small carvings or jewelry components. Because of its porous texture, Howlite can be easily dyed to imitate other minerals, especially turquoise because of the superficial similarity of the veining patterns. Howlite is also sold in its natural state, sometimes under the misleading trade names of "white turquoise" or "white buffalo turquoise", or the derived name "white buffalo stone". Sometimes Howlite fluoresces a blue, yellowish white or off white color under shortwave UV light and dissolves in hydrochloric acid solution without bubbling.

June 2010 Mineral of the Month

Prehnite

Prehnite is the first mineral ever to be named after a person, and was first described in 1789 for an occurrence in Haslach, Harzburg and Oberstein, Germany., It is named for Colonel Hendrik Von Prehn commander of the military forces of the Dutch colony at the Cape of Good Hope from 1768 to 1780. Prehnite is a member of the silicates family of minerals. It is brittle with an uneven fracture and a vitreous to pearly luster. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its color varies from light green to yellow, but also colorless, blue or white. It is mostly translucent, and rarely transparent. Though not itself a zeolite, it is found associated with minerals such as datolite, calcite, apophyllite, stilbite, laumontite and heulandite. It occurs in veins and cavities of basaltic rocks and sometimes in granites and gneisses. Prehnite crystallizes in the orthorhombic crystal system, and most often forms as stalactitic or botryoidal aggregates with only just the crests of small crystals showing any faces. There are no commercial uses for Prehnite other than collecting, carving and jewelry making. This, of course, makes it the perfect lapidary material for rockhounds.

May 2010 Mineral of the Month

'Spinel'

The name Spinel comes from the Latin word ‘spina’ meaning ‘thorn’ in reference to its sharp sided crystals. Spinel is a member of the oxides mineral group. Spinel crystallizes in the isometric system; common crystal forms are octahedral, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5-4.1 and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but is usually various shades of red, blue, green, yellow, brown or black. There is a unique natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. Some spinels are among the most famous gemstones: Among them is the Black Prince's Ruby and the 'Timur Ruby' in the British Crown Jewels, and the 'cote de Bretagne' formerly from the French Crown jewels. The Samarian Spinel is the largest known spinel in the world, weighing 500 carats. True spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones in Afghanistan and in Mogok, Burma. Recently gem quality spinels were found in the marbles of Luc Yen in Vietnam, the Mahenge and Matombo regions in Tanzania, the Tsavo region in Kenya and in the gravels of Tunduru in Tanzania and Ilakaka in Madagascar. Spinel is found as a metamorphic mineral, and also as a primary mineral in igneous rocks. In these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminum. Aluminum oxide may form as the mineral corundum or may combine with magnesium to form spinel. This is why spinel and ruby are often found together.

April 2010 Mineral of the Month

CHRYSOPRASE

Chrysoprase is a gemstone variety of chalcedony (a cryptocrystalline form of silica) that contains small quantities of nickel which provide it with its apple green to deep green color. The darker varieties of chrysoprase are also referred to as prase. The word chrysoprase comes from the Greek chrysos meaning 'gold' and prason, meaning 'leek'. As with all forms of chalcedony, chrysoprase has a hardness of 6 - 7 on the Mohs hardness scale and a conchoidal fracture like flint. The best known sources of chrysoprase are Queensland, Western Australia, Germany, Poland, Russia, Arizona, California, and Brazil. The chrysoprase and Ni silicate ore deposit in Szklary, Lower Silesia, Poland, was probably the biggest European chrysoprase occurrence and possibly also the biggest in the world. Chrysoprase was used by the Greeks, Romans, and the Egyptians in jewelry and other ornamental objects and because of its semi-opaque green color; it is often mistaken for Imperial jadeite. One of the most valuable chalcedony gem stones, chrysoprase is prized for its color and rarity. The stone occurs in serpentine rocks and in weathered materials of nickel ore deposits as nodules or in veins within the host rock

March 2010 Mineral of the Month

Hemimorphite

Hemimorphite is a sorosilicate mineral which has been mined from days of old from the upper parts of zinc and lead ores, chiefly associated with smithsonite. It was often assumed to be the same mineral and both were classed under the same name of calamine. In the second half of the 18th century it was discovered that there were two different minerals under the heading of calamine - a zinc carbonate and a zinc silicate, which often closely resembled each other.

The silicate was the rarer of the two, and was named hemimorphite because of the hemimorph development of its crystals. This unusual form, which is typical of only a few minerals, means that the crystals are terminated by dissimilar faces. Hemimorphite most commonly forms crystalline crusts and layers, also massive, granular, rounded and reniform aggregates, concentrically striated, or finely needle-shaped, fibrous or stalactitic, and rarely fan-shaped clusters of crystals.

Some specimens show strong green fluorescence in shortwave ultraviolet light and a weak light pink fluorescence in longwave UV.

Hemimorphite most frequently occurs as the product of the oxidation of the upper parts of sphalerite bearing ore bodies, accompanied by other secondary minerals which form the so-called iron cap or gossan. Hemimorphite is an important ore of zinc and contains up to 54.2% of the metal.
Hemimorphite is a member of the silicates group. Its hardness is 4-1/5 to 5 on the Mohs scale. It has an uneven to conchoidal fracture and a perfect cleavage. It can be white, colorless, blue, greenish, gray, yellowish or brown and has a colorless streak. It is transparent to translucent with a vitreous luster. It will give off water when heated in a closed tube and is soluble in acids with gelatinization.

February 2010 Mineral of the Month

Mica Group

Zinnwaldite Biotite

The word "mica" is thought to be derived from the Latin word micare, meaning "to glitter", in reference to the brilliant appearance of this mineral especially when in small scales.

The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having highly perfect basal cleavage. The five most common Micas are: Phlogopite, Biotite, Zinnwaldite, Lepidolite and Muscovite. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.

Phlogopite Lepidolite

Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites. Until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dramatically dropped when large reserves were found and mined in Africa and South America during the early 1800s. The largest sheet of mica ever mined in the world came from a mine in Denholm, Quebec, Canada. Scrap and flake mica is produced all over the world. Flake mica comes from several sources: the metamorphic rock called schist as a by-product of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Sheet mica is considerably less abundant than flake and scrap mica. Sheet mica is occasionally recovered from mining scrap and flake mica. The most important sources of sheet mica are pegmatite deposits.

Muscovite

Mica has several industrial uses including “Isinglass Mica” which are sheets of mica used as peepholes in boilers and lanterns because they are less likely to shatter compared to glass when exposed to extreme heat. Mica has a high dielectric strength and excellent chemical stability, making it a favored material for manufacturing capacitors for radio frequency applications. It is also used as an insulator in high voltage electrical equipment.

January 2010 Mineral of the Month

SULFUR

Named from the Middle English word 'sulphur' meaning brimstone. Crystals are usually yellow to yellowish-brown blocky dipyramids with thick tabular and disphenodal crystals being less common. Native sulfur is usually formed from volcanic action as a sublimate from volcanic gasses associated with realgar, cinnabar, and other minerals. It is also found in some vein deposits and as an alteration product of sulfide minerals. It can also be formed biogenically, a major source being salt domes, where it has formed by the bacterial decomposition of calcium sulfate.

Sulfur is a member of the native elements group and has a hardness of 1-1/2 to 2-1/2 on the Mohs Scale. Its specific gravity is 2.0 to 2 .1. Sulfur has a resinous luster and an imperfect cleavage with an uneven to conchoidal fracture. Its chemical composition is S

Sulfur fuses at the relatively low temperature of 113 degrees and gives off choking fumes of sulfur dioxide when burned. There are many industrial uses of sulfur ranging from matches and fireworks to rubber.