Rock Picture of the Week Archive 2
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Photo by Jim Bryan
Gypsum (CaSO4-2H2O) is usually formed from evaporating sea water or sulphate waters disolving limestone and comes in a variety of forms. We find it in most of our fossil hunting areas, usually scattered on ridges and side hills of clay where the clay has eroded away. This form is often mistakenly called mica because it is so clear. Gypsum contains a lot of water and if you heat it until it turns white and crush it, you will have Plaster of Paris. The name "Gypsum" itself comes from the Greek word for plaster.
Photo by Jim Bryan
Artinite (Mg2(CO3)(OH)2-3H2O is found in Serpentine areas and associated with Hydromagnesite. This specimen was found in the seams of a boulder in the quarry of an old asbestos mine. The crystals are little needles radiating from a point forming a cotton ball-like structure. Although they look soft and cuddly, the needles are very sharp, brittle, and easily crushed.
Photo by Jim Bryan
Cinnabar ( HgS ) On Quartz crystals. Cinnabar is an ore of mercury. Although very poisonous, it's bright red color led it to be used for pigmentation by native Americans. Realization of the environmental impact of mercury in recent years forced most of the producing mines out of business. This specimen came from the New Idria mine which was forced to shut down when the price of mercury dropped.
Photo by Jim Bryan
Melanite (Ca3Fe2Si3O12) is a black variety of Andradite Garnet. It's isometric crystals often give the appearance of cubes when viewed from certain angles. This specimen was formed in the metamorphic contact area between the ocean bottom and the continental land mass.
Photo by Jim Bryan
Chalcopyrite (CuFeS2) Appropriate for the first part of April, it is one of the minerals called Fool's Gold. It is easy to distinguish it from gold by scratching or smashing it. Real gold would be malleable while Chalcopyrite is brittle. It is a major ore of copper and even gold.
Photo by Jim Bryan
Selenite Rosettes (CaSO4-2H2O) are flower-like crystals of gypsum often found in oceanic clay deposits. This specimen was found in the Coalinga, California oilfields and is about the size of a baseball. There are a lot of variations in size and complexity of the rosettes.
Collected and Polished by Richard Menezes
Photo by Jim Bryan
Agate (SiO2) is a translucent variety of Chalcedony. It comes in many shapes and patterns. They and some other colorful stones were washed up on the beaches of northern California. The ocean waves and sand wore most of them smooth, making the polishing process a little faster and easier.
Photo by Jim Bryan
This Crab, similar to the
modern day
Sand
Crab, was
discovered when a sandstone nodule was cracked open. It lived about 3
to 5 million years
ago by the shore of California's inland sea. The nodule washed out of a
clay deposit and
is associated with Sand Dollars, Barnacles, and Snails.
The small white crystals in the body cavity are Calcite. The yellow is
probably Limonite
(rust), possibly from the iron in its blood.
Photo By Jim Bryan
Malachite (Ca2CO3(OH)2) is an ore of copper and often used as an ornament. Despite it's beauty, its usfulness in jewelry is limited due to its softness. It is often found on the fringe areas of volcanic activity or mountain upthrust where hot, metal rich gasses seep up through cracks and seams in the Earth.
Photo by Sharon Munford
Horn Corals were a solitary coral, this one dating from around 350 million years ago. They are fairly common in the limestone of Missouri. There are many types and sizes with ages varying by hundreds of millions of years.
Photo by Jim Bryan
Brachiopodia. This fossil, probably Reticulatia, was found in the Missouri limestone dating to about 325 million years ago. It measures about 2 inches wide.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Stibnite (Sb2S3) These crystals, some about 8 inches long, are an ore of the metal Antimony. It is fairly common in areas of volcanism or plate tectonics where cracks in the earth's crust allow hot vapors and liquids to seep up through the fissures and deposit metallic compounds.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Smilodon Californicus, often called "Sabre Toothed Cat", is the California State fossil. Smilodon lived in North and South America from about 1.8 million to 10,000 years ago. This one was recovered from the La Brea Tar Pits in Los Angeles CA.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Dolomite (CaMg(CO3)2) is generally formed from organic deposites in oceanic waters. It is used mainly as ornamental rock, ground cover, and in the production of cement and magnesium oxide.
Photo by Jim Bryan
This specimen is on display at the R.C. Baker Memorial Museum, in Coalinga, CA.
What happens when a lightning bolt hits the ground? If the conditions are right, such as electrical strength and soil type, it can actually melt the ground, turning it into a glass or ceramic. Sometimes it forms a melted core several feet deep.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Sulphur (S) (or Sulfur) on Aragonite. It is the biblical brimstone and is common in volcanic and hot spring areas. Also in areas where large bodies of water have evaporated. It has widespread use in manufacturing and agriculture.
Photo by Jim Bryan
This specimen is on display at the R.C. Baker Memorial Museum, in Coalinga, CA.
Desmostylus was a semi-aquatic herbivore that went extinct about 10 million years ago. It was related to the elephant, sea cow, and manatee. Although it is sometimes called a sea cow, it was more like the hippopotamus preferring fresh waters, in this case those of the central valley of California.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Hematite (Fe2O3) is the major ore of iron in the world. It is also the main source of the red color in rocks, soil, and even your blood. Although this specimen does not appear red, it is when reduced to a powder. It is sometimes mined for its use as a red pigment and often used as jewelry.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Adamite (Zn2AsO4(OH)) is a fairly rare mineral usually found in the upper, oxidized, portions of zinc deposits. In pure form it is colorless, but often is yellow or green due to impurities of iron or copper. Although it is too soft to be used as jewelry, it is popular with collectors because it fluoresces green in UV light.
Photo by Jim Bryan
This specimen is on display at the California State Mining and Mineral Museum in Mariposa, CA.
Aragonite (CaCO3)
is
less
common,
but
very similar to (and often mixes with) Calcite. Over time Aragonite
transforms into
Calcite. The speed of transformation is determined by the presence of
heat and water.
In pearls and many sea shells it is the source of the iridescent nacre
(mother of pearl).
It often fluoresces in UV light.