Silicon, Si, is the second most abundant element in the Earth’s crust after oxygen with an average abundance of 28.2% by weight or
282,000 ppm. It is such a common element that it forms over 1400 different mineral species within the very large silicates group, which
accounts for about a third of all known species.
Most silicon is used commercially without refining as in clays, silica sand and various stones with numerous large-scale industrial uses.
The elemental uses include various ferrosilicon alloys accounting for over 80% of world production for the ferrous foundry and steel industries. Other common uses are in Al alloys, chemical and glass industries, silicones, abrasives etc. Computer chips, electronics and
photovoltaic cells account for only a small percentage of silicon demand. Leading nations for silicon production are the USA, China,
Norway, Brazil, France, Iceland and India etc.
About 4 million tonnes of ferrosilicon and 500,000 tonnes of metallurgical grade silicon for semiconductors are produced annually. Since
in most previous articles in this series have included some of their most profuse members on Earth we will not have to include them here.
We first deal with native silicon followed by the rare silicides, which predominate in various kinds of meteorites that fall onto our planets
surface. Their inclusion is justified by the fact that there are many collectors of meteorites. The super abundant silica group (where industryextracts its silicon) that includes the most abundant mineral in the Earth’s crust will be discussed later in the series.
Silicon, Si, can be found as cubes, octahedrons or dodecahedrons up to about 1 mm in size and as thin iridescent films. Most other information has not been reported. It is transparent with a reddish tint and has a hardness of 7. The mineral occurs in with arsenopyrite, gold, calcite, graphite, pyrite, moissanite, quartz, native iron, xifengite, and linzhiite in a few ophiolites, andesite-basalt rocks, gneisses and as inclusions in gold from mantle, derived rocks. Chemical, methods are useful in its characterisation. Silicon specimens are known from various locations within countries such as Russia, China, USA, Cuba and Turkey.
Suessite, (Fe,Ni)3Si, is cubic mineral that forms anhedral interstitial vein fillings and as small cubic crystals. It is cream-white in reflected light, steel-grey in normal light, and is opaque. It is strongly ferromagnetic in character and possesses a high specific gravity of 7.0. The mineral is associated with olivine series minerals, pigeonite, kamacite, troilite, and khamrabaevite in highly reduced brecciated meteorites and in some basaltic porphyrites. X-rays and chemistry are best for identification. It has also been found in the Ir-Tash Stream Basin,
Arasham Mtn, Angren Region, Uzbekistan.
Nierite, Si3N4, occurs as lathlike crystals and is colourless with an adamantine lustre. It is extremely hard with a value of 9 and with a specific gravity of 3.1. The mineral crystallises in the hexagonal system. X-ray and chemical methods are used for certain recognition along with its elevated hardness value. Nierite is a very rare component of chondrite type meteorites and samples have been located within Algeria, Australia, Azerbaijan, China, and the USA. Typically it occurs with kamacite, perrryite, schreibersite, troilite, spinel,
chromite, hibonite, rutile and diamond.
Sinoite, Si2N2O, is another uncommon mineral of chondrite meteorites and is accompanied by enstatite, various nickel-iron alloys, plagioclase, troilite, pigeonite, daubreelite, oldhamite, alabandite, graphite and tridymite. Sinoite crystallises in the orthorhombic system
and forms lathlike crystals and granular aggregates. It is colourless and has a bright greenish-yellow cathodoluminescence. The
specific gravity is 2.8. X-ray and chemical methods are useful for characterisation. Again, it is found in various meteorites from Antarctica, Australia, Estonia, Finland, Germany, Poland, Pakistan, Sudan and Tanzania.
Xifengite, Fe5Si3, is hexagonal species that is steel-grey to grey in colour and is opaque. It possesses a metallic lustre and a black
streak. Its hardness is 5. The normal habit is as fine irregular grains to several mm in size. This mineral is strongly magnetic and has a specific gravity of 6.4. Chemistry and x-rays are needed for identification. Xifengite occurs in meteorites and in a few placers concentrating meteoritic materials. Associated species are kamacite, maghemite, magnetite, taenite, native silicon and wustite. This uncommon species has been found in placer concentrations from the Yanshan meteorite in the Yan Mts, Hebei Province, and the in Longquan Co, Zhejiang Province, both in China. It is also known from the Isovsky District, Middle Ural Mts, Russia.
Linzhiite, FeSi2, is steel grey in colour with a greyish black streak. It is brittle in character with a conchiodal fracture. The hardness is 6½ and has a metallic lustre. Irregular grains less than 0.5 mm size is the typical habit. Linzhiite is mineral of a few podiform chromite deposits with zangboite and native silicon. X-ray and chemical techniques are used to identify this mineral. Currently, this scarce mineral is known from only a few locations. Four of them are found in China within the Jiangsu, Shandong, Zhejiang Provinces, and in Tibet. Also from the Kaltat Creek area of the Targhasa massif, Russia, and the Zachativsk station, Donetsk, Ukraine.
Perryite, (Ni,Fe)8(Si,P)3, crystallises in the hexagonal system as narrow laths about 1 cm in length, and as tint blebs along grain boundaries. It is ductile in character with a pecific gravity of 7.6. Chemical and x-ray methods are required here. The mineral occurs in the environment of various iron and chondrite meteorites along with kamacite, troilite, schreibersite, and enstatite. Perryite is recorded from many countries including Antarctica, Australia, China, India, Pakistan, Yemen, Finland, France, Libya, Sudan, Malawi, South Africa
and the USA. It is quite probable that meteorite collectors will have this mineral as part of their collection.
Zangboite, TiFeSi2, occurs inheavy mineral separates from podiform chromitites in harzburgite within an ophiolite complex.
Accompanied species are native silicon and an unidentified Si-Fe-Ca mineral. It is orthorhombic in character forming tabular grains and irregular crystals that have a steel-grey colour with a conchiodal fracture. The hardness is around 5.5 and is brittle. It possesses a black streak and a metallic lustre. Its specific gravity is 5.0. The usual chemical and x-ray techniques are required to distinguish this very infrequent species. The sole locality for samples is the Luobusha mining district, Tibet, China.
We will commence with the renowned ubiquitous silica group of minerals in the next set of articles in this series.