News from the Geoblogosphere
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, a new tool to create lithological/sedimentological logs online..
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Geologic State Symbols Across America - Georgia
The next state up for the Geological State Symbols Across America is:
You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along).
Shark Tooth 1976
I also have some Geology of the National Parks Through Pictures that I have done for Georgia previously. These include:
Chickamauga & Chattanooga National Military Park
State Mineral: Staurolite
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating staurolite as the official State mineral... Whereas, Georgia has a wealth of minerals and gemstones; and Whereas, staurolite is a mineral found in old crystalline rocks and is particularly well known and abundant in north Georgia; and Whereas, staurolite crystals are known mostly as “Fairy Crosses” or “Fairy Stones”, and generations after generations have collected them for good luck charms; ... Whereas, the importance of Georgia’s minerals to the industrial growth and heritage of this State should be appropriately recognized. Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made:
(1) Staurolite is designated as the State of Georgia’s official mineral.... Approved May 18, 1976.
An example of a staurolite crystal showing the 60-degree penetrating twin cross.
Image from iRocks.com
Staurolite is a metamorphic mineral, meaning that it is formed from the increased heat and pressures that form metamorphic rocks, like gneiss or schist. Staurolite is part of the silicate group of minerals with a chemical formula of (Fe,Mg)2Al9Si4O23(OH). The mineral is usually brown to black in color with a vitreous (glassy) luster. It can be found in transparent varieties, however the most common variety is opaque. It is also rather hard, 7 to 7.5 on the Mohs Hardness Scale, meaning that is is on par with quartz, and resistant to weathering so it will often erode out of its host rock intact, ending up within sedimentary deposits of local rivers. The crystals of staurolite are what truly make it a unique mineral though. Commonly found as six-sided, elongated crystals, the most striking feature are the penetrating twinned crystals creating an "X" shape (60-degree angle crosses) or, less frequently, a "+" shaped cross (90-degree angle crosses). Even the name of "staurolite" comes from the Greek word for cross "stauros". Because of these twinned crystals, staurolite is sometimes referred to a "fairy crosses", because of the legend that at the death of Christ, the local fairies cried tears that crystallized into cross-shaped crystals. Within the US, there are a high abundance of staurolite crystals found at Fairy Stone State Park, Virginia, with the name based on the legend. There are relatively few actual uses for staurolite, because of the rarity of the mineral compared to other options. It was once used as an abrasive because of it's extreme durability, but other, cheaper sources are now used. The most common use now is as a decorative item or as jewelry due to its "mystical" properties and its cross-shape.
The geological regions of Georgia. Image from the Georgia Encyclopedia.
Within the state of Georgia, there are only a handful of locations and rock formations that contain staurolite. The state itself can be broken into five distinct geological regions, as seen on the map to the left. The Coastal Plain, Valley & Ridge, and Appalachian Plateau Regions are dominated by sedimentary rocks, and are therefore not where you would generally find staurolite. The Piedmont and Blue Ridge Regions though, are heavily rich in metamorphic and igneous rocks. In fact the counties within the north-central region including Cherokee, Fannin, Hart, Upson, and Warren Counties are your best bets for finding staurolite crystals (geologic map below). Within the Piedmont and Blue Ridge regions, there are certain formations that are the best ones for staurolites. The Great Smokey Group is a Late Proterozoic (~600-700 million years old) rock group that can be divided up into several distinct rock formations. Of which, the Copperhill, Dean, and Hughes Gap Formations all contain staurolite schist, staurolite-mica schist, and/or staurolite-garnet-mica schist interbedded with other metamorphic rocks. The Hughes Gap Formation is noted as having a few "spongy or stringy masses of staurolite" within staurolite zones. Since staurolite is resistant to erosion, the crystals have a habit or eroding out of the rock and accumulating on the surface or within nearby stream beds. The other major contributor of Georgia staurolites is the Mineral Bluff Formation, another Late Proterozoic metamorphic assemblage that includes a minor amounts of staurolite schist interbedded with other metamorphic rocks.
A highlight of the metamorphic rocks within northern Georgia. Image from the Georgia Geological Society.
Notable occurrences of staurolites from the Mineral Bluff Formation include the J.M. Spear farm near Ball Ground in Cherokee County. Notable occurrences of staurolites from the Hughes Gap and Dean Formations include the J. Fred Hackney farm near Blue Ridge and the E.D. Richars property near Mineral Bluff in Fannin County. Other notable localities include the towns of Royston, Thomaston, and Norwood. Detailed location data can be found within the Minerals of Georgia book on page 111.
State Gemstone: Quartz
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating ... quartz as the official State gem.... Whereas, Georgia has a wealth of minerals and gemstones; ... and
Whereas, quartz is the second most abundant mineral on Earth, and Georgia is blessed with a great deal of it in a wide variety of colors; and Whereas, quartz is the amethyst that has been most used in jewelry, and clear quartz when faceted resembles diamond; and Whereas, the importance of Georgia’s minerals to the industrial growth and heritage of this State should be appropriately recognized. Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made: ...
(3) Quartz is designated as the State of Georgia’s official gem. Approved May 18, 1976.
An example of a quartz crystal from Cold Water Creek, Rock Branch, Georgia.
Image from iRocks.com.
Quartz is one of the most common minerals on Earth, primarily due to its simple structure and chemical formula, SiO2. Quartz also has an extremely high hardness, 7 on Mohs hardness scale, meaning that it doesn't scratch very easily and therefore does not break down easily. As the rocks on Earth are slowly eroded over time, most of the other minerals will break down into clay while quartz grains will generally just gets smaller and smaller. The result is that most beach sand is composed of quartz that has a slight hematite (rust) stain to it to give the sand grains their slight yellowish color. Although quartz is a simple mineral, it can come in a variety of colors depending on what type of impurities are present in the crystal structure; pure quartz crystal is clear, milky quartz is white, smoky quartz is grey, amethyst is purple quartz, citrine is yellow quartz, rose quartz is pink, as well as some other colors and varieties. Quartz does not have any cleavage, meaning that when it breaks it doesn't form along perfect surfaces. Instead as the quartz crystals grow, individual mineral molecules of quartz are added to the outside of the crystal from water rich in dissolved SiO2 or mineral melt (liquid rock like lava or magma).
Here is a map of all of the known quartz crystal discovery locations. These include every possible range of colors in quartz from citrine to amethyst. Map courtesy of mindat.org.
The mineral quartz is pervasive throughout all crustal rocks, especially in coastal states like Georgia, since quartz is the primary component of sand. However, when designating "quartz" as the state gemstone, the government specifically mentioned amethyst (which is purple quartz) and "clear quartz when faceted resembles diamonds" (also known as quartz crystal). Like staurolite above, crystals of amethyst and clear quartz are generally only found in the northern half of Georgia, within the Piedmont and Blue Ridge Regions (as per the map to the left). One of the most publicized locations for mining amethyst is the Jackson's Crossroads Amethyst Mine located to the east of Athens. The mine is located with a rock known as a metadacite, which is a metmorphosed dacite. Dacite is a volcanic rock with a fairly high silica (quartz) content, located between rhyolite and andesite on the felsic-mafic scale. Being a volcanic rock, there are many holes (termed vugs) within the rock, allowing for the precipitation of quartz crystals over time. It is within these vugs that the amethyst is found. Although Jackson's Crossroads is a private mine, they do offer opportunities for public digging. Although the main attraction here are amethysts, clear quartz crystals can also be found in abundance within these sorts of mines. Besides just the metadacite, quartz crystals (including amethyst) can be found in a wide variety of the rocks in northern Georgia including gneiss, another metamorphic rock. These gneisses, formed from granite or shale, also had many vugs within them. Over time the quartz/silica within the gneiss got leached out by groundwater and started to precipitate within the vugs. As the mineral crystallized, it formed a consistent pattern and shape, which is the quartz crustal we all know and love. When the quartz crystals are found intact within the vugs, these are what are known as geodes. Other locations for amethyst crystals include Warrenton within some granitic gneiss, the Coldwater Creek area and the Chapman Mica Mine, both in Elbert County, and near Tate City in Pickens County. While amethyst is generally not widely available, other varieties of quartz, especially clear quartz crystals, can be found all over the northern half of Georgia as seen in the quartz crystal location map above.
State Fossil: Shark Tooth
Act of Georgia General Assembly March 18, 1976 OFFICIAL STATE MINERAL, FOSSIL, AND QUARTZ DESIGNATED. No. 104 (House Resolution No. 517-1385). A Resolution. Designating ... the shark tooth as the official State fossil...; and
Whereas, the shark tooth is a relatively common fossil in Georgia and in fossil form can be traced back 375,000,000 years; and
Whereas, the teeth are especially prized for fossil collectors and range in color from the more common blacks and grays to white, brown, blue and reddish brown; ...
Now, therefore, be it resolved by the General Assembly of Georgia that the following designations are hereby made: ...
(2) The shark tooth is designated as the State of Georgia’s official fossil.... Approved May 18, 1976.
A variety of fossil shark teeth, representing the multiple possible colors. Image from the Florida Museum by Jeff Gage.
Within the fossil record, sharks have a fairly long history. Scientists have fossil shark material that dates back over 420 million years ago during the Silurian. However, there is very little of a shark that is typically preserved. In general, the skeleton of sharks, as well as all chondrichthyans, which includes rays and skates, are made up of cartilage. Cartilage is a material that breaks down very quickly and hardly is ever fossilized. Fossilization is the process where organic material is turned into stone by a one-to-one replacement of the organic material with more permanent minerals such as silica (quartz) or calcite. The fossilization, or permineralization, process causes the teeth to be a wide variety of colors depending on the elements within the water that replaced the organic materials. Even a little of something, such as iron, can turn a normally white item into a very rich red color. Cartilage, however, breaks down very quickly and so the fossilization process does not typically occur. However, there are several features of a shark that can be preserved with the teeth being the most common. Shark teeth are made up of dentin, a material harder and denser than bone, and covered with an enamel shell. On top of that, sharks typically go through tens of thousands of teeth a year. So one shark could potentially produce 50,000 teeth over its lifetime. Fossilization potential also exists for the denser cartilaginous sections of the shark skeleton as well, just not as highly as the teeth. These include the dense core of the vertebrae, parts of the jaw, the rostral (nose) node, and on some sharks, the spines. Dermal denticles are another fossilization potential. They are tiny pieces of bone that are scales on the outer surface of the shark skin.
Teeth from the shark
showing the wide variety of teeth even within one shark specimen. Image from fossilguy.com.
Shark teeth, however, can tell us a lot and not very much about the shark. Shark teeth are amazingly varied, even within a shark. Look at the picture above to the right. The teeth can vary in males to females, in juveniles to adults, in the top and bottom jaws, as well as where they are located within the jaw. Therefore, by just finding the teeth it is nearly impossible to determine how many species once existed because the teeth aren't attached to anything anymore (the jaws tending to all degraded away), or even what species an individual tooth came from. Loose teeth are also very difficult to date. The only real indicator of the age of a shark tooth is to find the sedimentary rock bed that it came from and date that. The one exception to that rule is the shark
, more commonly referred to as just Megalodon. Due to the extreme size of their teeth, they are actually fairly easy to identify. However, a full jaw of Megalodon teeth has never actually been discovered and all representations of them are completely made up by people who think what they might have looked like. In general, shark teeth can be a fairly abundant and cool fossil collectible, depending on the local fossil collecting regulations. Sharks are vertebrates and therefore would fall under any vertebrate fossil collecting restrictions.
Map of Georgia Counties with fossils found within them. Rock age range of the Coastal Plain ranges from Cretaceous (grey) to Holocene/Modern (tan). Map from Georgiafossils.com.
Unlike the state mineral and the state gemstone, which are both primarily found within metamorphic or igneous rocks, fossil shark teeth are found primarily within sedimentary rocks. And the best place to locate them would be the southern region of the state known as the Coastal Plain (according to the map above). The rocks in the Coastal Plain Region range from Cretaceous to the Holocene/modern day. The rock units that fossil shark teeth are found in is generally marine limestone, however they have been found in other rocks and materials as well including younger unconsolidated sediments (not compressed and cemented into rocks yet). One location that has turned up an abundance of fossil shark teeth are the man made islands along the southern Savannah River. These islands are composed of dredged sediment from the Savannah River, so although the islands contain an abundance of fossils, the material isn't much use scientifically since they had been heavily transported from their primary site of deposition 19 million years of deposits mixed together. Oligocene fossil shark teeth have been found further inland in the limestone deposits of the Ocmulgee Formation, located within the Oaky Woods Wildlife Managment Area. Finally, some of the oldest shark teeth in Georgia can be found within the Cretaceous age Eutaw Formation alongside pterosaur fossils and the Blufftown and overlying Cusseta Formations. These teeth largely represent an extinct species of goblin shark, where the shark has essentially a pronounced overbite. Besides these there are likely thousands of individual instances of shark fossils found across the southern half of Georgia and it is no wonder why the shark tooth was decided upon as the state fossil. However, as I stated before, sharks are vertebrates and often fall under strict collecting rules so before you go out collecting fossils, make sure you are aware of the local rules and regulations and are following them appropriately.
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