Thursday, August 07, 2014

Geological State Symbols Across the US - #5 California

The next state up is California. Here are the stats:

                                                                                        Year Established
State Rock: Serpentine                                                             1965
State Mineral: Gold                                                                 1965
State Gemstone: Benitoite                                                        1985
State Fossil: Smilodon fatalis (saber-toothed cat)                    1973

State Rock: Serpentine

    California was the first state to identify a state rock, serpentine. Serpentine is a green to black, fibrous and platy, metamorphic rock. It was metamorphosed from the ultramafic (dark green minerals like olivene) rock peridotite. It was named for the serpent skin-like pattern formed by the multitude of greens throughout the rock. The original parent rock, peridotite, was deposited in the ocean, below the basalt and other crustal rocks. The high heat, water, and high pressure converted the peridotite into serpentine. Serpentine itself is often composed of three main minerals, chrysotile (often found in the form asbestos), lizardite, and antigorite, among others.

   California was formed by the accretion of various islands and oceanic material as the North American plate moved westward and the subduction zone along the west coast of North America allowed material to be "scraped" off of the subducting plate. These accretionary provinces contained large pockets of serpentine within them, providing California with an abundance of valuable serpentine minerals including chromite, magnesite, cinnebar, and most importantly at the time, asbestos. For this reason, as well as its soft nature making it an easy stone to polish and usage as an ornamental rock, it was designated as California's state rock.

    However, due to the strong association of serpentine with asbestos, there has been recent urges to change or remove the state rock. Having the state rock associated with cancer is not something many lawmakers agree with. Scientists contend though, that asbestos within its natural state is harmless. Only when powdered, can asbestos become a carcinogen. Currently it is unsure whether the rock will be removed as the state rock.

State Mineral: Gold    

     The chemical symbol for gold is Au, and gold is one of the unique minerals that, in its pure form, is composed entirely of one element. It has a hardness of 2.5 to 3 on the Mohs hardness scale meaning that it actually is very soft (your fingernail is 2.5). For this reason most gold jewelry is mixed with another metal to prevent scratching and bending easily. The karat rating of the gold represents it's purity, where 24 karat is 99.9% pure, 22 karat 91.7%, 18 karat 75%, and so on. Gold naturally does not corrode or tarnish, so even when it is mixed with other metals it usually has a resistance to tarnishing, enhancing its value for jewelry. When gold is found in place, the highest grade of gold is found in association with quartz veins, as the one shown to the left from Placerville, California.

     Along with the identification of a state rock, California also identified a state mineral at the same time, gold. It is not hard to understand why. Gold was initially discovered in California in 1848 at Sutter's Mill in Coloma. This discovery eventually brought on the Gold Rush of 49' (the name of the 49ers are based on this gold rush as well). The Gold Rush increased the number of people in California from pre-1849 to post-1849 100 times (going from less than 1,000 to over 100,000). The discovery of gold and sudden influx of people to California, caused it to have statehood decades before most of the other western states. Overall, two billion dollars worth of gold was extracted from the state during this time period. The current slogan for California, "The Golden State", is due to this foundation on gold.

     California's gold mines (current and historic) cover the entire state and can be found from the very southern border all the way to the northern border, with almost every county having at least one. Due to the high specific gravity of gold (high density) and its resistance to oxidizing (tarnishing) as it is eroded out of the mountains it concentrates in rivers in what are called placer deposits. It is from these deposits that people find gold while they perform the famous "wild west" practice of panning for gold.

State Gemstone: Benitoite
Benitoite from Benitoite Gem Mine, San Benito County, California (Type Locality for Benitoite)

     Benitoite is an extremely rare mineral where the only gem quality stones are found in California. It is often found as a blue to dark blue mineral but can be purple, pink, white, and colorless. The mineral also fluoresces blue under ultraviolet light. Bernitoite is a barium titanium silicate (BaTiSi3O9) that often forms pyramidal crystals, although the crystals are usually 5 cm or less in size. It was initially found near the headwaters of the San Benito River, in San Benito County and was named for its discovery location.

     When benitoite was originally discovered it was thought to be another variety of sapphire. However, further analysis by some jewelers ruled out the gem as a sapphire. In 1907, George D. Louderback, identified and named the  unique and very rare mineral. Primarily bentitoite is known as a collector's item with a small amount of samples being used to align and adjust electron microprobe beams. Benitoite is found within natrolite veins that are interlayered with serpentine. Benitoite forms from the hydrothermal altering of the serpentine, a primary mineral found within the state rock, serpentine.

     However rare and valuable the gem is, collectors and rockhounds have the unique chance to collect their own specimens of benitoite by going to the California State Gem Mine. Where, for a fee, you can try and find some of the gems yourself.

State Fossil: Smilodon fatalis (saber-toothed cat)
     Smilodon fatalis, more commonly known as the saber-toothed cat, is an animal that went extinct around 13,000 years ago, towards the end of the last ice age. The saber-toothed cat is known from North America and the Pacific regions of South America. The reason that this animal was chosen for the state fossil of California is that over 1,200 different specimens have been found in California, primarily within the Rancho La Brea asphalt deposits (the tar pits) and is the second most common animal found there.

     Although, often depicted as living in caves, Smilodon fatalis is more commonly found within plains or woodland deposits, and likely lived as am ambush predator. The skeleton of Smilodon supports this theory, since it is robust with a short tail, indicated it did not run down its prey. Originally it was though that the saber teeth were used to grapple and hold on to the prey, however they are not strong enough to do this and would result in a lot of broken teeth. It is now hypothesized that the saber teeth were used to deliver a mortal stab wound while the animal then waited for its prey to die.

    The La Brea Tar Pits, where the fossils are primarily found in California, formed from the crude oil that seeps to the surface and partially evaporates, leaving only the heavy tar behind. Animals would get stuck  and eventually enveloped by the tar after they died from lack of food or water. The tar pits where known to the Native Americans in the region and were used as glue and waterproofing their boats and houses. In the early 1875 though, the fossil of a saber-toothed cat was found and described.


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