Petrified Wood, Geodes, Crystals, Agates and Carvings

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Agates mostly occur as nodules in volcanic rocks or waters containing Silica in solution which is possibly derived from the decomposition of Silicates in the lava.  The Siliceous matter is deposited in regular layers resulting in the banded or striped formation.  It is very unlikely that you would ever find an exact duplicate of any type of Agate, Brazilian or other.

Brazilian Agate Stand Up

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Quartz is the second most common mineral in the Earth's continental crust.  It is mainly composed of Silica or Silica based minerals.  Although Quartz is known by a variety of names, the most important distinction between types of Quartz is that of macro-crystalline, individual crystals visible to the unaided eye, and micro-crystalline, where aggregates of crystals are only visible under high magnification.  There are many forms of Quartz including Chalcedony, Amethyst, Citrine, and Carnelian which are results of mineral impurities or heat treatments.

Quartz Crystal

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Amethyst is a purple variety of Quartz often used as an ornament.  Upon exposure to heat, Amethyst generally becomes yellow, which some refer to as Citrine or "burnt" Amethyst.  It occurs in color from a light, slightly pinkish violet to a deep grape purple.  It is widely distributed as a mineral, but fine, clear specimens that are suitable for cutting as ornamental stones. 

Amethyst

Petrified Wood is a type of a fossil as it consists of fossil wood where all the organic materials have been replaced with minerals while retaining the original structure of the wood.  These minerals are most often Silicates such as Quartz.  Other minerals, Manganese, Iron and Copper, in the water or mud during the petrification process give Petrified Wood a variety of color ranges: black - Carbon; green/blue - Copper; red/brown/yellow - Iron.  Petrified Wood can preserve the original structure of the wood in all its detail all the way down to the microscopic level.  Structures such as tree rings and the various tissues are often observed features.  Although Petrified Wood can be found worldwide, it is rather rare in larger quantities and at times can be difficult to obtain by the average collector.

Nebraska Petrified Wood

PR605b   This is a pretty Frog carved from Soapstone.  The frog has a second frog carved inside the outer. It is a beautiful multi-color Green with lighter accents.  It measures 4 1/2"x 3 3/8" x 2 1/8" tall and is nicely polished except for the bottom.  A very nice addition to any polished collection or it would make a great gift.

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Soapstone, also known as Steatite or Soaprock, is a metamorphic rock or Talc-Schist.  It is composed of the mineral Talc and is rich in Magnesium and is formed by the metamorphism of ultramafic protoliths and the metasomatism of siliceous Dolostones.  It is a very soft material and may have a soapy feel when touched.  It can be easily carved into decorative items as well as bowls or other cooking utensils.  It is used by welders and fabricators as a marker due to its resistance to heat.

Soapstone Frog

PR614c   Here is a very cool Green Calcite Free Form from Mexico.  It has many, many crystals in various shades of green. It measures nearly 6 3/4" x 4 3/4" x 4 1/4" and has a nice polish.  A very unique gift for someone special or add it to your own collection.

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Calcite is a Carbonate mineral that is most widely distributed on the Earth's surface.  It is a common constituent of sedimentary rocks with Limestone in particular.  A Calcite formation can take on many different shapes and sizes which is dependent on the location, ground water occurrence and temperature.  Calcite is usually white or colorless but can be gray, red, yellow, green, blue, violet, brown or black.  The deeper the color is usually indicative of the definitive impurities from the earth or water.

Green Calcite

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Marble is a metamorphic rock consisting of Limestone but mostly composed of Calcite.  It is used extensively for sculpture, building materials and has many decorative uses.  The pure white Marble is probably the most common form known, but the characteristic swirls and veins of many colored Marble varieties are usually due to various mineral impurities such as Clay, Silt, Sand, Iron Oxides or Chert.

Black Zebra Marble

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Agates mostly occur as nodules in volcanic rocks or waters containing Silica in solution which is possibly derived from the decomposition of Silicates in the lava.  The Siliceous matter is deposited in regular layers resulting in the banded or striped formation.  It is very unlikely that you would ever find an exact duplicate of any type of Agate, Brazilian or other.

Brazilian Agate Crystal

This lovely specimen was found in the South Dakota Badlands near the Cheyenne River. It was cut and polished in the Rock Shed's own Lapidary Department.  A must have for the fossil collector or an excellent gift for someone!

Be sure to click on the pictures at right to see the full size versions.

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South Dakota Fossil Coral
 

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Rhodocrosite is a Manganese Carbonate mineral.  It is typically a rose-red color, but impure specimens can be shades of pink to pale brown.  It is used as a key component of low-cost stainless steel and certain Aluminum alloys.  Quality banded specimens are often used for decorative stones and jewelry, although it is relatively soft and difficult to cut.

Rhodocrosite

PR608b  This is a great find!!  Here is a very nice, above average quality Labradorite specimen.  It measures3 3/4" x 2 1/4" x over 3/4" and has a good polish on all sides.  This specimen has a good color mix with a highly iridescent shine.  The specimen has some areas of Biotite Mica that shows up dull black. This would make a great gift for the "hard to buy for" person. 

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Labradorite is a Feldspar mineral that occurs in large Crystal masses in Anorthosite and shows an iridescence or "play of colors."  Gemstone varieties of Labradorite exhibiting a high degree of iridescence are Spectrolite, Moonstone and Sunstone.  High quality samples with good iridescent qualities are desired for jewelry.

Labradorite

PR612b   This is a pretty Pakistani Onyx Vase with a nice polish.  It measures 3 3/4" x 3 3/4" and has a good color scheme and very different design.  This Vase would make a great addition to any polished collection or it would make a great gift.

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Onyx is a banded variety of Calcite.  The colors of its bands range from white to almost every color except shades of purple, blue and black.  It is used for vases, bowls, beads, cabochons and other items.  This type of Onyx is found in Mexico and Pakistan.  It is often carved, polished and sold in a variety of different things. 

Onyx Vase

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Agates mostly occur as nodules in volcanic rocks or waters containing Silica in solution which is possibly derived from the decomposition of Silicates in the lava.  The Siliceous matter is deposited in regular layers resulting in the banded or striped formation.  It is very unlikely that you would ever find an exact duplicate of any type of Agate, Brazilian or other.

Brazilian Agate

PR610c  This is a pretty, nice quality covered Jar made from Chinese Marble.  It measures 4 1/4" with the lid on x nearly 4" in diameter and is nicely polished.  It has an unique design which exhibits several colors and designs in different areas of the jar.  Definitely something special for that special, hard-to-buy for person.

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Marble is a metamorphic rock consisting of Limestone but composed mostly of Calcite.  It is used extensively for sculpture, building materials and has many decorative uses.  The pure white Marble is probably the most common form known, but the characteristic swirls and veins of many colored Marble varieties are usually due to various mineral impurities such as Clay, Silt, Sand, Iron Oxides or Chert.  This type of Marble will often have small animal like creature fossils throughout the matrix or media.

Covered Marble Jar

PR607c   This is a very nice Picture Sandstone slab from Arizona.  It measures over 4 1/4" x 3 3/8" x 3/8" and has a smooth, unpolished finish.  These slabs are very unique in shape and size and would enhance any mantle, desk top or wall.  It comes complete with a plastic display stand.

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Sandstone is a sedimentary rock composed mainly of sand size mineral or rock grains.  Most Sandstone is composed of Quartz and/or Feldspar because these are the most common minerals in the earth's crust.  It can be almost any color.  The Sandstone beds often form highly visible cliffs and are strongly identified with certain regions of the world.

Picture Sandstone Slab