Natural Glasses 

 Natural glasses are made up mostly of silica and come in a variety of shapes and compositions. Even now, the exact origins of several natural glassware are unknown. Many are faceted and used as ornaments, while some are big, transparent pieces. The chemical makeup of obsidian varies greatly, however it can include up to 77 percent silica and 10–18 percent alumina. If quartz, feldspar, and mica had developed instead of obsidian, the rock would have been quartz, feldspar, and mica.

 

Obsidian

Obsidian is generated by the quick cooling of volcanic lava, which would have acquired a crystalline structure if allowed to cool slowly. Some obsidians have a network of curved fractures that may be seen. The resultant texture is perlitic, and disintegration along the fractures results in bead- or ball-shaped particles. These pieces have been given the name marekanite, which is derived from a Siberian location. Peanut obsidian is another name for a similar mineral from Mexico that creates spherulitic patterned obsidian with radiating feldspar threads. This may be located in the Sonora neighbourhood.

Obsidian is often opaque black or grey, although it may also be yellow, crimson, or greenish brown. It may have an iridescent shine created by reflections from minute impurities, as seen in silver and golden obsidians, which are frequently polished into necklace beads. In the United States, a kind of obsidian with spherulitic inclusions of a white mineral on a black background groundmass has been cut and polished. This is known as 'flowering' obsidian. A variation with black and red bands has been dubbed'mountain mahogany,' and it is sometimes used for decorative goods and carvings. Although translucent leaf-green obsidian has been suggested, green is an extremely unusual colour, and most clear green obsidians are moldavites or just green glass. There have been reports of red and blue obsidian.

Moldavite

Moldavite is composed of roughly 75% silica and 10% alumina, and it may also contain oxides of iron, potassium, calcium, sodium, magnesium, titanium, and manganese. The hardness is close to 5.5, the SG is 2.30–2.50, and the RI is 1.48–1.52. The absorption spectrum, with its hazy bands in orange and blue, is of little use in identifying the substance. The only fluorescence seen under X-rays is a weak yellowish green. Moldavite has many spherical or torpedo-shaped bubbles with swirls and striae; the crystallites observed in obsidian are lacking here. Marekanite has also been used to Mexican material. 'Apache tears' are elegant pebble-like solid cores of unmodified glass, 25 mm or more across, from the decomposed obsidian of the American southwest.

When transparent ones are sliced, they form grey or light grey stones with fine silky striations that give the stone a cat's-eye impression. The name 'Tokay lux-sapphire' refers to a brown-black obsidian from Hungary.

Chemical and Physical Properties

The hardness of obsidian is close to 5. Obsidian fracture is notably conchoidal, and it is because of the ease with which the material can be broken into sharp-edged flakes that obsidian was so valued by Stone Age people who lived in areas where obsidian was abundant, the easily controlled flaking allowing the production of keen-edged spear points, knives, and tools.

The lustre of obsidian is vitreous; the RI ranges from 1.48 to 1.51, but is often near 1.49. Thin pieces examined between crossed polars reveal that the material's groundmass is isotropic, but the field is speckled with brilliant spots of light due to very minute crystalline particles, which are common in volcanic glass. Obsidian's SG ranges from 2.33 and 2.42, at least for the varieties used in jewellery.

When a tiny sliver of obsidian is studied under a microscope, the texture is shown to be a transparent glassy ground with numerous microscopic crystallites. These can have circular bodies (globulites), rod-shaped bodies (belonites), or coiled or twisted hair-like bodies (trichites). They may be fused into chains (margarites), most likely in a fictitious parallel to a string of pearls. It may be necessary to use a rather high magnification to remedy the issue.

these organs Some obsidian has round or torpedo-shaped bubbles. These, which may be seen clearly with low-power magnification, are frequently in parallel arrangement, and it is this parallelization of the bubbles and crystallites that gives certain obsidian its valued gloss.

Occurrences

Obsidian is found all over the world, however the majority of the material used in jewellery comes from North America. The Glass Buttes in Lake County, where iridescent material is discovered, and Hampton in Deschutes County, Oregon, are both significant locations. Obsidian has been mined at Obsidian Cliff in Yellowstone National Park in Wyoming since the days of the North American Indians, who utilised it for arrowhead construction. Obsidian deposits may be found in Arizona, Colorado, and Nevada, and the material has been mined in California since prehistoric times. Glass Mountain in Modoc County, Little Lake in Inyo County, and Obsidian Butte on the south-west side of Salton Sea in Imperial County are the most well-known of these Californian sources. Apache tears are most common in New Mexico.

The Aztecs and their forefathers employed obsidian for the sharp points of their weapons, mirrors and masks, and adornment. Because of its multiple use, they termed the substance iztli and surnamed it teotetl (divine stone). Humboldt unearthed the ancient Aztec obsidian pits in Sierra de la Navagas in the Mexican state of Hidalgo in the early nineteenth century. Obsidian may also be found in several other locations in Hidalgo, as well as in the Mexican states of Jalisco, Queretaro, Michoacan, and Vera Cruz. The Maya got their obsidian from old quarries in La Joya, some 30 kilometres east of Guatemala City, while the Equadorians had a quarry near Guamani.

Basalt Glass

Basalt glass is semi-translucent to opaque and generally black or brown in colour. It is found mostly on the cooled rims of basaltic intrusions or lining or filling vesicles or holes in basalt. It includes around 50% silica. When struck with a hammer, basalt glass, which has a hardness of around 6, does not yield big flakes or show significant conchoidal fracture, but instead breaks up into little irregular shards and splinters. The RI of these glasses is between 1.58 and 1.65, while the SG is between 2.70 and 3.00.

The texture seems homogeneous at low magnification, and the structure cannot be observed till magnified at a high magnification. Basalt glasses are not often cut as gem material, however few experimental cabochons have been created from light grey, navy-blue, bluish green, and brown chunks discovered in the headwaters of the Flinders River in northern Queensland. The pieces are frequently mottled and spotted, which adds to their appeal.

Meteorites

 meteorite is a fragment of a destroyed star body that, while travelling through space, collided with the earth's gravitational field and landed on its surface; hence, it is said to be of cosmic origin. Meteorites are classified into two types: those composed mostly of iron and nickel, known as siderites, and those composed primarily of olivine, pyroxene, and a trace of feldspar, and so resembling basaltic rocks in composition. These are known as 'aerolites.'

It is unlikely to find meteorites in the world of diamonds. However, one form of alleged meteorite has been employed for adornment.

The Gibeon meteorite is one of the most popular meteorites used for jewelry. It was discovered in Namibia and is believed to have landed on Earth around 30,000 years ago. The meteorite is composed mostly of iron and nickel, and it displays a unique crystalline pattern known as Widmanstätten patterns, which are formed due to the slow cooling of the metal over millions of years in space.

The Gibeon meteorite is often used for making rings, pendants, and other jewelry pieces. It is highly valued due to its rarity and distinct appearance, and it serves as a unique reminder of the vastness and mystery of the universe.

Tektites - Gemstones from the Sky

While meteorites and diamonds are fascinating, those who study gems are interested in a different type of substance with a glass-like constitution rich in silica, known as tektites. These fragments, which are assumed to be of meteoritic origin, were first discovered in 1787 in western Moravia and in Ceské Budejovice near the Bohemian river Moldau, which is known in Czech as the Vltava.

The fragments were dubbed moldavites after the river's old name, and they are translucent green, greenish brown, or brown in color. They are frequently strangely fissured on the surface, resembling alpine terrain with jagged mountain summits or rounded crests with a botryoidal surface.

The substance was cut into gemstones, yielding bottle-greenstones. Cut moldavite has been marketed under a number of elegant and entirely deceptive names, including "bottle stone," "obsidian," "water chrysolite," and "pseudo-chrysolite." The stone has also been referred to as bouteillenstein.

These gemstones from the sky are truly unique and serve as a reminder of the incredible power and mystery of our universe.

Czech moldavites are classified into three types. Oval or spherical specimens from the Radomilice district of southern Bohemia are pale or translucent bottle-green with less embedded bubbles and a less visible flattened surface. These are silica-rich and alumina-deficient, with very little lechatelierite (i.e. near the silica glass composition).

Moldavites from the majority of other southern Bohemian findings are bottle-green, flattened, and brimming with bubbles. Their lechatelierite concentration is greater, with Si, Al, and Fe content that is halfway between the first kind and a form found in Moravia, coloured brown and containing more Al and Fe than other types. Moravian specimens are round and contain fewer bubbles. There have been four separate occurrences documented. Some can be discovered in Upper Miocene sediments, while others can be found in Pliocene and Pleistocene strata. The rest is made up of slope lavas, perhaps Pleistocene, and Holocene or Pleistocene alluvia.

Australites are button-shaped glass fragments discovered in South Australia and Tasmania. Billitonite was discovered on Billiton Island between Sumatra and Borneo, and specimens are dark brown.

These tektites are fascinating in their variety and origins, each telling a unique story about the history of our planet and the universe beyond.

Colombia generates colourless tektites, but regardless of origin, they are button-shaped. The Jukes-Darwin field in Queenstown, Tasmania, yields silica-rich and alumina-poor colourless to olive-green to black specimens with SG 1.85–2.30 known as darwinite or queenstownite.

Crater Glass

There are other varieties of natural glasses that, while not meteoritic in origin, have their origins in meteoritic activity. One variety is derived from meteoritic craters, where the glass is made by the extreme heat generated by a meteor's impact on the earth's surface when the surface cover is siliceous, such as in a sandy desert.

Such glass, which might be white, greenish yellow, or black in colour, is essentially a fused quartz with around 90% silica and certain impurities, the most common of which is iron. The substance is sluggish and densely packed with vesicles. The SG of these glasses ranges from 2.10 to 2.31, which is lower than the SG range of the previously described moldavites and tektites.

The value is frequently lower than that of pure fused quartz (silica glass, 2.203), most likely due to the inclusion of vesicles. The RI ranges from 1.46 to 1.54, with high values owing to a high iron content. This crater glass has been discovered in a variety of locations, the most of which are recognised for their sandy deserts, such as Wabra in Saudi Arabia, Henbury in central Australia, and Meteor Crater in Arizona, USA.

Fulgurites and Trinitite - Natural and Man-made Glasses

Fulgurites, also known as lightning tubes, are narrow tubes of fused sand formed by the high heat created when a lightning flash strikes and enters the desert sand. These glass tubes can be found in various sizes and colors, depending on the type of sand and the intensity of the lightning strike. They are often considered to be natural works of art and are collected by enthusiasts from all around the world.

Trinitite, on the other hand, is a man-made glass that was formed by the high heat generated by the experimental atomic bomb that was fired in New Mexico in 1945. This substance is vesicular and greenish in color, and its constants are comparable to those of conventional crater glass. Much of this fused sand is still radioactive after many years.

Although it may appear implausible that such material would be used for adornment, it has been documented that some trinitite has been fashioned into diamonds — mostly as publicity for film stars. Given the radioactivity present, wearing such things for an extended length of time would very probably pose a risk.

 

Libyan Desert Glass - A Mysterious Natural Glass Found in the Sahara Desert

Desert Glass is a nearly pure silica glass that is found in the wastes of the Libyan desert. This mysterious glass was discovered in 1932 and is still not fully understood by scientists today.

The glass is found as sand-blasted lumps up to 7 kg in mass. It is of a greenish-yellow color and is usually cloudy rather than clear due to the inclusion of vast numbers of irregularly shaped vesicles. The origin of the glass is uncertain, but it is believed to have been formed by the impact of a meteorite or by a volcanic eruption.

Desert Glass has been used for centuries by the indigenous people of the Libyan desert to make tools and weapons. It is also highly valued by collectors and scientists for its unique properties and mysterious origin.

Studies of Desert Glass have revealed that it contains high levels of iron, magnesium, and other elements that are not commonly found in silica glass. This has led scientists to speculate that the glass was formed by a unique process that is not yet fully understood.

Silica Glass is a unique type of glass that consists of nearly pure silica with a refractive index of 1.46, a specific gravity of 2.21, and a hardness of 6 on Mohs’ scale. It has a vitreous lustre and a dispersion of 0.010. However, the stones cut from this material lack brilliancy and are not attractive due to their insipid tint.

Occasionally, spherulites of the cubic modification of quartz known as cristobalite are found included in silica glass as strings or as single individuals. Some of the material has been cut and polished for collectors, but its poor brilliancy does not make it popular in the gemstone industry.

Furnace slag is a glassy material that is typically striped with greyish blue and dark brown or black. It has an SG near 2.82 and looks like an obsidian, but it is actually a byproduct of furnace operations. This material has been compared with a green glass reportedly made from ash from the Mount Saint Helens eruption in 1980, which gave an RI of 1.508 and an SG of 2.448. The black sample showed a variation over the range 1.500–1.526 and an SG of 2.485. It was concluded that the green glass contained from 5 to 10% of Mount Saint Helens ash at most.

A transparent brownish natural glass from San Luis Potosi, Mexico, showed layered and botryoidal textures giving rise to an iridescent effect. Similar material has been described, misleadingly, as iris opal. IR spectroscopy showed that SiOH groups were present but that water was not.

Libyan Desert Glass (LDG) is a naturally occurring glass that is found in areas in the eastern Sahara Desert. The glass is characterized by its yellow-green color and is thought to have formed from a meteorite impact. The origin of the glass has been discussed in a book by J. McCall (Tektites in the geological record, 2001: ISBN 1862390851) who suggests that it may be impact-related and that the glass originated in two craters both just over 100 km from the strewn field.

The glass is believed to have formed around 26 million years ago. It is thought to have been created by a meteorite impact that occurred in the area. The impact would have caused the sand in the region to melt and fuse together to form the glass. The glass is found in a strewn field that covers an area of around 6,000 square kilometers. The glass is highly valued by collectors and is used in jewelry and other decorative items.