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SILICATES

Our appreciation on this page, by material was from the book or websites of the following sources. You may want to click on the websites above to see what else each has.

You may also want to visit our page on Quartz.

See below for some of our website pages which have examples of silicate minerals.


The chemical formula for all silicates is SiO² which stands for a molecule which is comprised of 1 atom of Silicon and 2 atoms of Oxygen Silicon dioxide. Opal is another Silicate whose formula is SiO² · nH²O called Hydrous silica which often has some iron and aluminum. Opal has an addition amount of water which varies up to 10%.

The silicates constitute the largest and most common class of minerals. This mineral is sometimes totally transparent (as in optical quartz) but mostly translucent, at least in thin layers or splinters. Silicates are on the average harder than most minerals and have a lower specific gravity.

Water is present in many of them, especially in the zeolites, where the water is loosely bound. In other Silicates, the water is strongly bound and cannot be removed except with the destruction of the mineral itself.

All silicates contain the silicate atomic structure, regardless of how simple or complex a given mineral may be. A tetrahedron is the fundamental building block of all silicates. One silicon atom is surrounded by four oxygen atoms.

The construction is something like this: The four sided tetrahedron in the isometric crystal system, in this case the one silicon atom is inside the tetrahedron, at the center. The four oxygen atoms are at the four corners of the tetrahedron. The number and manner of linking of the silicon-oxygen tetrahedrons is the basis upon which the different silicate minerals are formed.

Specific forms of Silicates include quartz, which comes in many forms.Quartz is the most abundant single mineral on earth. It makes up about 12% of the earth's crust, occurring in a wide variety of igneous, metamorphic and sedimentary rocks.

Quartz generally has a hardness of 7 on the mohs scale and has hexagonal crystals (six-sided). The crystals usually are prismatic, striated crosswise and frequently terminated by double rhombohedrons (like hexagonal pyramids). However, some forms of quartz are also granular, disseminated, and massive. They generally have no cleavage, but may rarely have indistinct rhombohedral parting. the Specific gravity is 2.65 and the fracture is conchoidal.

Quartz varieties are commonly separated into two groups based on the size of the individual grains or crystals; macrocrystalline quartz in which individual crystals are distinguishable with the naked eye, and cryptocrystalline quartz in which the individual crystals are too small to be easily distinguishable under the light microscope.

The cryptocrystalline varieties of quartz may be separated into two types; fibrous and microgranular. Chalcedony is the general term applied to the fibrous cryptocrystalline varieties. Agate is an example of a fibrous cryptocystalline banded Chalcedony variety of quartz. Carnelian, Chrysoprase and bloodstone are other Chalcedony varieties.
Chert is the general term applied to the microgranular cryptocrystalline varieties of quartz, of which flint and Jasper are examples.

Some of the quartz forms are: (NOTE: some of which are semi-precious stones)

Quartz is basically as clear as glass. In fact, glass is made of quartz, with a smattering of other chemicals. When dug up in Arkansas as your Curator has done, it may be the color of the background, behind the word QUARTZ, above. The next step is to put it into a plastic tub Oxalic Acid for a week or two in the hot sun, and voila, you have beautiful crystal clear quartz.

We will be filling in a good bit of information on this vital mineral (in fact without quartz, the silicon chip in the computer composing this page, could not operate.

You are directed to a page on ARKANSAS QUARTZ, from whence comes some of the most finest and clearest quartz crystals.

For Smoky Quartz crystals, visit our page on the PIKE NATIONAL FOREST. This is a beautiful gem stone quality quartz.

Until we get all of our own specimens online, we express our greatest appreciation to our friend Jo Edkins in the U.K. who has given us permission to use her specimens on our website. So here are some examples of Silicates, for your recognition and enjoyment.

Most graphics on this website, can be enlarged to a full view by clicking on the graphic.
However, those with an * in front of the mineral name cannot be enlarged by clicking on the Graphic.


CRYSTAL FORMS OF SILICATE

Amethyst Citrine in white matrix Rose Quartz Rutilated Quartz
Quartz crystal burr
(PMNS specimen)
[you can click to enlarge]
Quartz Crystals
Double terminations
(PMNS specimen)
[you can click to enlarge]
Smoky Quartz crystal
(PMNS specimen)
[you can click to enlarge]
Lone Star cut
Quartz Crystal
Found by T.W. Proctor
Cut by William O. Proctor


NON-CRYSTAL FORMS OF SILICATE

Agate
Slice sawed through
a Geode
Aventurine Bloodstone Carnelian
(a/k/a Cornelian)
Chrysoprase
(a/k/a Chrysophase)
Flint Jasper Moss Agate
Opal Sardonyx Tigereye Geode
this is a crystal form

Sometimes minerals look quite different in situ (i.e. in the ground) and right after you bring them out of the ground compared with after they are cleaned and ready for display.

Here is a sample to compare the beautiful Arkansas quartz crystal 'burr' (where the points are in every direction) right out of the ground (left) and after it has had an acid bath for a couple of weeks in the hot sun (right).

[this is the same crystal burr shown above, only a larger view than above--click on either picture to see full screen view].

Quartz 'Burr' before acid bath Quartz 'Burr' after acid bath