Rock Picture of the Week Archive 3

Rhodochrosite (MnCO3) is a minor ore of manganese. It is a member of the Calcite group of minerals common in manganese deposits and also occurs in hydrothermal vents. Despite its softness, the rose red and pink colors make it popular as decorative items and jewelry.

Azurite (Cu3(CO3)2(OH)2) is a very minor ore of copper. It is usually associated with (and over time weathers into) Malachite.
Because of its widespread availability, historically it was often used as a blue pigment. The bright blue color gives it a high ornamental value, but its softness and sensitivity to heat and light tends to limit its use in jewelry.

Halite (NaCl), is common table salt. It is normally obtained by evaporating sea water, but is also found in many inland lakes that have no outlet and are subjected to evaporation. There are also deposits of underground salt where ancient ponds have evaporated.
Historically it was used as a food preservative and was very valuable. The Romans sometimes paid their soldiers in salt, from which the word "salary" was derived.

Aquamarine (Be3Al2Si6O18) is a pale blue variety of Beryl, named for its sea water color. Other noted varieties are Emerald (green) and Morganite (pink). It often appears as large crystals and its color and hardness make it a valuable gemstone.
Common Beryl is a major source of the metal beryllium.

Emerald (Be3Al2Si6O18) is a green variety of Beryl, and is one of the most valuable gemstones. Other noted varieties are Aquamarine (pale blue) and Morganite (pink). The majority of the worlds Emeralds come from Columbia.
Common Beryl is a major source of the rare metal beryllium, similar to aluminum, and is used mainly in alloys.

Morganite (Be3Al2Si6O18) is a pink variety of Beryl, but the color can vary from orange-peach to pale violet. Other noted varieties are Aquamarine (pale blue) and Emerald (green).
It was discovered in 1911 and named after the financier (and gem collector) J. P. Morgan.
Most of today's gems come from Brazil, Madagascar, Afghanistan, or the U.S.A.

Atacamite (Cu2Cl(OH)3) is a fairly rare mineral formed in the oxidized portions of copper mines, usually under arid conditions, and is a minor ore of copper.
The color is dark green (often Emerald green), but is too soft and brittle to use as a gemstone.

Ruby

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Ruby (Al2O3) is the red or pink, and most valuable, variety of Corundum. All other colors are called Sapphire. It sometimes has inclusions of Rutile oriented on the crystal axes forming a six legged star when viewed from the proper angle.
It is the second hardest mineral found in nature and is used as a gemstone. It also has widespread use in abrasive and polishing compounds.

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Shark Teeth

Photo by Jim Bryan

Teeth are just about the only part of the shark that will fossilize, since their skeletons are mainly cartilage.They are distributed in oceans world wide and have been collector items throughout history.
Sharks teeth have changed very little over millions of years, proving that it is an efficient design. These are about 3 to 5 million years old.

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Pyrite Dollar

Photo by Sharon Munford

Pyrite (FeS2) Dollars are generally found in shale near coal mines. The shale layers restrict them to a two-dimensional growth.
If you purchase one beware of the specimens that are iridescent, as they are probably treated with bleach. Treated ones, although beautiful, will usually start to decompose within months and give off sulfuric acid.

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Silver

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Silver (Ag) is sometimes found as pure metal and sometimes compounded with other minerals, but the majority of it comes from alloys of other metals.
Silver has the highest conductivity of eletricity and heat of any metal. Among other things, it is used in electrical circuits, jewelry, and photography. Although seldom used, it also has antiseptic properties.

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Microcline

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Microcline (KAlSi3O8) belongs to the Feldspar group of minerals. Although it is usually pink, white, or gray, it can also occur in other colors, such as the blue in this specimen. It is a very common mineral and is widespread in igneous rocks.
Microcline is hard enough to be used in jewelry and is often used as decorations.

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Epidote

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Epidote (Ca2FeAl2(Si2O7)(SiO4)(O,OH)2) is common, mainly in metamorphic and contact area rocks. The color grades through shades of yellow, green, brown, and black depending on it's chemical makeup. The amount of the minerals Ca, Fe, and Al vary and are even replaced with other minerals at times.
Epidote is hard enough to be used in jewelry and decorations, and sometimes as faceted gemstones.

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Crab Claws

Photo by Jim Bryan

These crab claws were left stranded on the beaches of California's prehistoric inland sea about 3 to 5 million years ago. The claws and shores can be found in places where continental drift has broken and tilted the valley floor exposing the layers.

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Uvarovite

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Uvarovite (Ca3Cr2(SiO4)3) is a calcium-chromium Garnet of green, often Emerald, color. It is fairly rare and usually found as a fine crystal coating on its matrix.
Crystals large and clear enough to be faceted as a gemstone are extremely rare, but jewelry is sometimes made by using clusters of drusy crystals.

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Topaz

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Topaz (Al2(F,OH)2SiO4) is hard, heavy, and makes fine gemstones. Although the name is usually associated with the color yellow, it comes in many other colors including blue, green, and red. The colors can also be changed by subjecting it to heat treating and irradiation.

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Velvet Malachite

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Malachite (Ca2CO3(OH)2) is usually found in the upper, oxidized portions of copper veins. The velvety texture of this specimen is due to the fine hair-like crystals covering it. This one came from Bisbee Arizona.

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Sand Dollar

Photo by Jim Bryan

Sand Dollars are a variety of echinoderms, in this case dendraster, and are close relatives of sea urchins. These skeletal remains of them are called the test. When alive they were covered with short movable spines.
Although nearly five million years old, they are nearly indistinguishable from their modern day relatives.

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Borax

Photo by Jim Bryan

This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.

Borax (Na2B4O7+10H2O) is created by repeated evaporation of lakes. It is soluble in water and often used as a cleaning agent.
Due to its loose bond with water, in dry environments specimens (including this one) will lose some of their water and alter to Tincalconite.

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