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!
SILICON specimens:
(hover for more info)
SILICON specimen sii-1
$ 36.00
Dims: 5.5 x 4.69 x 2.5" (13.9 x 11.8 x 6.3 cm)
Wt: 1 lb, 5.3 oz. (603 g)
(laboratory-grown)
This intriguing piece consists of a large, amorphous chunk of raw Silicon that was originally grown in a laboratory. It appears to be made up of many smaller pieces that have been fused together. The Silicon has the silvery-gray color, metallic luster and low density that are standard for such material. One face appears to have undergone some oxidation during the fusion process, as it is coated with a thin, cracked layer of clear glass.
no photo
sii-1 ($ 36.00)
(laboratory-grown)
SILICON specimen sii-6
$ 39.00
Dims: 4.56x2.79x2.33" (11.59x7.09x5.91cm)
Wt: 25.82oz (732g)
(lab grown, probably USA)
Actually, this chunck of pure silicon does not look like the usual single-crystal boules used to manufacture computer chips, but rather like a bi-product of that process (forming on the walls or floor of the over, or crystallizing when the melt is allowed to cool). One side of the specimen is nearly perfectly flat, except for a detailed pattern of ridges that look like crystals forming on the surface of a melt that has cooled. On the opposite side is an area that looks like a cavity within which some distinct crystals have formed, although I do not see how this could have happened in the lab, unless this is an artifact of the production of pure silicon from a slag containing other components that maintained a molten space within which the crystals could form.
no photo
sii-6 ($ 39.00)
(lab grown, probably USA)
SILICON specimen sii-7
$ 36.00
Dims: 4.51x3.11x3.04" (11.46x7.91x7.73cm)
Wt: 15.77oz (447g)
(lab grown, probably USA)
This is a most unusual specimen of silicon. Generally, we see common boules used to make computer chips, or sometimes re-melts of ship components, but this is different. The outside is rough, a texture imposed by the container in which it formed, except for the narrow bottom (in the image) which is quite smooth but with some texture (almost like it was spray-painted). The inside (see the top view) has the typical feel and luster of silicon boules, with a concentric and somewhat hollowed-out growth pattern that defies my understanding of how it could have formed. There is a moderate amount of damage, almost entirely to the thin, fragile edges of the rim. I do like this oddity.
no photo
sii-7 ($ 36.00)
(lab grown, probably USA)
SILICON specimen sii-8
$ 42.00
Dims: 5.06x5.04x5.02" (12.86x12.80x12.76cm)
Wt: 41.45oz (1175g)
lab grown, USA
This is the tip of a silicon boule, used to make computer chips. It is perfectly round and the cone shape varies in width in a sinusoidal pattern. The surface of the silicon has striations, caused by uneven pulling rates from the molten silicon bath from which it was grown. It appears to have been pulled exactly a millimeter at a time, and the length of time at each stage determines the width of the resulting boule. It was cut flat at the base but not polished, and there is some damage, probably caused by the discarding of the now usless tip of the boule - the really valuable part is the long uniform width part that they slice into wafers for computer chips.
no photo
sii-8 ($ 42.00)
lab grown, USA
SILICON specimen sii-3
$ 40.00
Dims: 3.96x3.85x2.77" (10.06x9.79x7.04cm)
Wt: 27.13oz (769g)
lab grown, USA
This is the tip of a silicon boule. The rest of the crystal may have been used for memory or computer chips. While showing no crystal form, boules like this are grown as large single crystals so that crystal defects are at a minimum. Numerous fracture areas near the edges reveal a conchoidal fracture pattern and a very bright luster. The sides of the specimen show an interesting stepped growth pattern, showing the steps as the boule was pulled from the melt.
no photo
sii-3 ($ 40.00)
lab grown, USA
SILICON specimen sii-4
$ 36.00
dims mm=97.32x66.70x65.58
wt g=80
lab grown, USA
This neat little specimen of pure silicon has the shape of a top, although I don't recommend spinning it. The "handle" end shows the typical striations caused by the stepwise pulling from the melt, and the bottom is a nearly perfectly smooth reflecting convex surface.
no photo
sii-4 ($ 36.00)
lab grown, USA
SILICON specimen sii-5
$ 30.00
dims mm=108.54x66.86x57.99
wt g=599
lab grown, USA
I'm not sure how this specimen acquired its shape. My best guess is that molten silicon was poured into a container with a textured side wall, then gradually cooled and cracked near the center. Individual crystals are visible, as fine acicular growths generally in a radial pattern, plus the center has radial "collumns" likely caused by cracks upon cooling.
no photo
sii-5 ($ 30.00)
lab grown, USA
 

Copyright ©1995-2023 by Amethyst Galleries, Inc.