Silicon

Chemical formula: Si

Native silicon is a rare, crystalline form of the element silicon, found mainly in specific volcanic conditions.

## Characteristics Native silicon is a chemical element and a mineral from the native elements group. It occurs as small, usually microscopic, isometric crystals with octahedral or cubic forms. It often forms granular aggregates, lamellae, or dendritic aggregates. Its surface can be dull or covered with a coating, but on a fresh fracture, it exhibits a strong, metallic luster. It is opaque and has a dark gray or black color. ## Physical Properties Silicon is characterized by a hardness of 6.5-7 on the Mohs scale, which makes it a relatively hard mineral. It has a strong, metallic luster on fresh surfaces. It is brittle, and its fracture is uneven to conchoidal. Its density is approximately 2.33 g/cm³. ## Colors and Varieties This mineral occurs in dark gray, steel-gray to black colors. It does not form color varieties. It is important to distinguish it from the much more common synthetic silicon produced on a mass scale for the electronics industry, which often has iridescent oxide coatings on its surface. ## History and Name The name silicon comes from the Latin word "silex" meaning flint, a hard stone. The element was first isolated and described by Jöns Jacob Berzelius in 1823. As a mineral, native silicon was first described in 1904 by Henri Moissan. Its status as a distinct mineral was approved by the IMA in 1983. ## Uses Native silicon has no industrial application due to its extreme rarity. It is solely an object of interest for collectors and scientists. Industry relies entirely on synthetically produced high-purity silicon.

Properties

Mohs hardness: 6.5-7
Luster: Metallic
Streak: Black
Density: 2.329
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Native silicon is identified by its metallic luster on a fresh fracture, high hardness, regular crystal forms (if visible), and relatively low density for a metallic-looking mineral. Dark gray or black color and a black streak are also characteristic. ## Distinguishing from Similar Minerals It can be confused with graphite, which is, however, much softer (hardness 1-2) and leaves a mark on paper. From most sulfides (e.g., galena), it is distinguished by its significantly lower density and greater hardness. Synthetic silicon often has unnaturally large sizes and iridescent coatings, rarely found on natural specimens. ## Crystal Forms It crystallizes in the isometric system, forming small, well-formed octahedra and cubes. It also occurs in granular aggregates, lamellar forms, and as dendrites.

Geological environment

## Genesis Native silicon is a high-temperature mineral. It forms under strongly reducing conditions, most often as a product of volcanic exhalations (fumaroles), where hot volcanic gases react with rocks. It is found in lavas and volcanic tuffs. It can also form in contact metamorphic zones under the influence of magmatic intrusions. ## Mineral Associations It co-occurs with other minerals formed under similar conditions, such as moissanite (silicon carbide), graphite, native iron, pyrite, and also with minerals from the zeolite group. ## Localities The most important occurrences of native silicon in the world are volcanoes on the Kamchatka Peninsula in Russia (including Tolbachik volcano), where the best-formed crystals have been found. It has also been reported in Spain (near Huelva), in the USA (Arizona), and in the Pamir Mountains in Tajikistan.

Rarity

Very rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, sharp-edged crystals with a distinct, metallic luster. Crystal groups embedded in a natural rock matrix are particularly sought after. Crystal size is a key factor – any specimen with crystals exceeding a millimeter is considered exceptional. Surface purity, lack of mechanical damage, and confirmed natural origin (as opposed to ubiquitous synthetic material) are crucial. ## Popular Localities By far the most desirable specimens come from the fumaroles of Tolbachik volcano in Kamchatka, Russia. This is where most of the world's best crystalline native silicon specimens available on the collector's market originate.

Care and storage

## Cleaning Specimens of native silicon are generally stable. They can be cleaned with compressed air to remove dust. If necessary, distilled water and a soft brush may be used, followed by thorough drying of the specimen. ## What to Avoid Avoid contact with strong chemicals, especially hydrofluoric acid, which reacts with silicon. Despite its high hardness, it is brittle, so it should be protected from impacts and drops. ## Storage Store in stable conditions, away from dust and moisture. It is best to keep it in a closed display box or cabinet to prevent scratches from harder minerals and protect it from mechanical damage.