Libyan Desert glass

Chemical formula: SiO<sub>2</sub>

Libyan Desert Glass is a natural siliceous glass of a pale yellow color, likely formed as a result of a meteorite impact in the Sahara Desert.

## Characteristics Libyan Desert Glass (LDG) is a natural impact glass, consisting almost entirely of pure silica (lechatelierite). It occurs as irregular, wind-abraded fragments with a characteristic pale yellow to greenish-yellow color. The surface of specimens is often rough, pitted, and matte due to eons of sandblasting (corrasion) in the desert. The internal structure is usually homogeneous, glassy, although it may contain small gas bubbles and rare mineral inclusions, such as cristobalite. ## Physical Properties The hardness is approximately 6-7 on the Mohs scale, which is similar to quartz. The luster is vitreous, and the material is usually translucent, rarely transparent. The density is significantly lower than most minerals, at about 2.2 g/cm³, which makes specimens feel light relative to their size. ## Colors and Varieties The dominant and most desired color is intense yellow. Pale yellow, milky white, and greenish hues are also found. The material is homogeneous and does not form named commercial varieties; it is classified solely based on color quality and transparency. ## History and Name The name comes directly from its occurrence location – the Libyan Desert, on the border between Libya and Egypt. This material was already known in ancient Egypt. Evidence of this is a scarab carved from Libyan Desert Glass, placed in the pectoral of Pharaoh Tutankhamun, dating its use to approximately 1300 BCE. The first scientific description in Western literature comes from Patrick Clayton in 1932. ## Uses Beyond its immense scientific importance as evidence of a prehistoric impact, Libyan Desert Glass is a prized collector's material. The purest and most transparent fragments are sometimes cut and used to create unique jewelry.

Properties

Mohs hardness
6-7
Luster
Vitreous
Streak
White
Density
2.2
Fracture
Conchoidal
Transparency
Transparent to translucent

Diagnostic features

## Identification Libyan Desert Glass is relatively easy to identify. Key features include: low density (it is very light), characteristic yellow color, glassy internal structure, and a typical, pitted and matte external surface. The presence of gas bubbles and any darker inclusions is also a diagnostic feature. ## Distinguishing from Similar Materials It can be confused with other tektites (e.g., moldavite), which, however, usually have a darker, green or brown color and a different surface sculpture. From ordinary, artificial glass, it is distinguished by its irregular shape, signs of corrasion, the presence of inclusions (e.g., cristobalite), and specific chemical composition. Citrine (a variety of quartz) is much heavier and crystalline, not amorphous. ## Crystal Forms As a natural glass, it is an amorphous substance and does not form crystals. It occurs exclusively in the form of irregular lumps, fragments, and pieces with abraded edges.

Geological environment

## Genesis The most accepted theory suggests that Libyan Desert Glass formed approximately 29 million years ago as a result of a large meteorite or comet impact in the sands of the Western Desert. The extreme temperature and pressure of the explosion led to the melting of silica-rich sands, which then rapidly solidified in the atmosphere, forming glass. No impact crater has yet been found, suggesting it may have been an airburst (as in the Tunguska event), which dispersed the molten material over a vast area. ## Mineral Associations Within the glass, high-temperature mineral inclusions such as cristobalite and baddeleyite can be found. Desert sand, mainly quartz, occurs on the surface and in the crevices of specimens. ## Localities The only confirmed occurrence is the Great Sand Sea area in the Libyan Desert, on the border between western Egypt and eastern Libya. All collector material comes from this single, extensive strewn field.

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued specimens are those with an intense, pure yellow color, high transparency, and a minimal amount of internal bubbles or inclusions. Large, undamaged fragments with an interesting, aerodynamic shape (though rare) also fetch higher prices. Milky, whitish, or less intensely colored specimens are rated lower. ## Market Prices Prices range from a few to several tens of dollars per gram, depending on quality. Small, multi-gram fragments are commonly available. Prices rise sharply for specimens over 50-100 grams, and large, transparent fragments with intense color can command very high prices in the collector's market. ## Popular Localities All material originates from one area – the strewn field in the Libyan Desert. Collecting material is currently strictly controlled and restricted by the Egyptian government, which affects its availability and price on the market.

Care and storage

## Cleaning Specimens can be safely cleaned with lukewarm water and mild soap, using a soft brush to remove sand and dust from crevices. After washing, they should be thoroughly rinsed, preferably with distilled water, and allowed to air dry completely or gently blotted with a soft cloth. ## What to Avoid Avoid contact with strong chemicals, especially hydrofluoric acid, which etches silica. Despite its relatively high hardness, the glass is brittle and susceptible to fracturing from sudden temperature changes (thermal shock) and impacts. It should not be cleaned in ultrasonic cleaners. ## Storage Specimens are best stored in separate, padded boxes or on stands to prevent scratches and chips from harder minerals. The material is stable and does not fade under sunlight, so it can be displayed in illuminated showcases.

Sources

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