THE MINERAL SILICON

• Chemistry: Si, Elemental Silicon
• Class: Elements
• Subclass: Semi-metals
• Group: Carbon
• Uses: As an integrated circuit (IC) substrate and semiconductor.
• Specimens

Silicon is rarely found in nature in its uncombined form. In fact it is amazing how rare native silicon is with 25.7% of the Earth's crust being silicon. Silicon, binds strongly with oxygen and is nearly always found as silicon dioxide, SiO₂ (quartz), or as a silicate (SiO₄^-4). Silicon has been found as a native mineral only in volcanic exhalations and as tiny inclusions in gold.

Of growing interest in rock shops, however, are laboratory-grown silicon boules. Most such specimens are end fragments or flawed discards from the integrated circuit industry. Silicon boules are grown (pulled) from a molten state from a seed crystal, in such a way as to produce a single large crystal which must be completely without crystal defects, or the entire boule must be discarded. Modern techniques can create a single crystal several feet long and up to 10 inches in diameter. These large crystals are sliced into very thin wafers, upon which complex integrated circuits can be etched. The unused parts of the boule are often saved, and used as paperweights or sometimes cut into bookends or other decorative items.

The word silicon (which is taken from the latin word for flint) can be confused with other terms. One of these terms was already mentioned: Silicate (SiO₄^-4). Silicates are minerals whose primary cation is the SiO₄^-4 ion group. Another confusing term is silica. Silica is a term used by geologists for SiO₂ or silicon dioxide in any form whether it is in the form of quartz, or any of the Quartz Group members, or as a segment of the chemistry of a silicate, or even as silicon dioxide dissolved in water. A geologist might use the phrase, "The magma was rather poor in silica." Indicating an SiO₂ content that was lower than expected. Yet another term is silicone. Silicone is a synthetic polymer that is made of silicon, carbon and oxygen and has many medical and some industrial purposes.

PHYSICAL CHARACTERISTICS:

• Color is iron-black, dark silver-gray to bluish brown.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits are limited to microscopic crystals and inclusions.
• Cleavage is absent.
• Fracture is conchoidal.
• Hardness is 7.
• Specific Gravity is approxiamtely 2.3.
• Streak is black
• Other Characteristics:
• Associated Minerals are limited to gold in which silicon has been found as inclusions.
• Notable Natural Occurrences include Nuevo Potosi, Cuba; Tolbachik, Kamchatka and Kola Peninsula, Russia.
• Best Field Indicator: Found with computer circuits etched on the surface!