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NOW FOR YOUR VIEWING PLEASURE…
SANTOS CRATER AGATE
PATAGONIA, ARGENTINA
MENDOZA BUTTE
FINEST SOUTH AMERICAN STONE
AGATIZED CORAL
BOTRYOIDAL EYES, VUGS, UNDERGROWTH
RED to BLACK
PSEUDOMORPHS
OF JASPER, RYOLITE, CHALCEDONY & HEMATITE
ITS GOT IT ALL GOING ON.
3.5" x 2.5" x 1.5"
POLISHED FACE
9.6 ounces / 272 grams
OLD STOCK
from the
BOB & NANCY HICKS RANCH
Inventory # 148
Excerpt from Bob's Rocks / Story by Lance Strong
...Luis de los Santos, an Argentine native, as the discoverer.
De Los Santos found crater agate in 1997, and--like the Puma--he discovered it while he was prospecting near petrified-wood fields. I thought it was named for the open craters of botryoidal-looking red interiors, but De Los Santos told me it was named for the ancient volcano where he collects this material at an elevation of 6,000 to 7,000 feet, and the matrix is rhyolite.
Patagonia is the region of southern Argentina south of the Colorado River and east of the Andes Mountains. (In older publications the term Patagonia refers also to the southern parts of Chile.) In 1902, the division of Patagonia occurred between Chile and Argentina. It is about 250,000 square miles in area, and consists of desert plateaus including the eastern section of Tierra del Fuego, the archipelago located off the southern tip of South America.
They show a thin revetment of red jasper. The agate walls are a translucent, smoky chalcedony with inclusions of fine red hematite lines. De Los Santos says the Crater agate is strongly green-fluorescent due to uranium salts...
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FYI
Agate is a cryptocrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.
Etymology and history
The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the river Achates (Greek: Ἀχάτης) in present-day Sicily, sometime between the 4th and 3rd centuries BC. Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now called Dirillo.
Ancient use
Agate is one of the most common materials used in the art of hardstone carving, and has been recovered at a number of ancient sites, indicating its widespread use in the ancient world; for example, archaeological recovery at the Knossos site on Crete illustrates its role in Bronze Age Minoan culture.
Formation and characteristics
Most agates occur as nodules in volcanic rocks or ancient lavas, in former cavities produced by volatiles in the original molten mass, which were then filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls. Agate has also been known to fill veins or cracks in volcanic or altered rock underlain by granitic intrusive masses. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section. Such stones are known as banded agate, riband agate and striped agate.
In general, agates form when silica in groundwater is deposited in openings in the subsurface. It is generally believed that Montana agates were formed as the result of volcanic activity in the Yellowstone Park area millions of years ago, which deposited a tremendous amount of silica-rich ash over a wide area. Some Montana agates, such as “limb casts”, appear to have originated from wood that became buried by ash and fossilized after the volcanic activity.
Credit: Dr. Roger Pabian of Nebraska State University
It's probably safe to say that all Montana agate has been transported many miles from its original location. The transport process has tumbled the agates along the streambed, and weak or cracked rocks have either fallen apart or else the cracks have been “healed” by exposure to the silica-rich waters of the Yellowstone River.
One of the most attractive features of Montana agate is the colored inclusions, which are made up of minerals (such as iron and manganese). These inclusions form when mineral-laden water is “wicked” into the rock through cracks or fractures and the mineral content of the water is deposited within the rock. (more about internal structure of Montana agate)
The highest-quality Montana agate is free from cracks or “checks”. Some of the most beautiful Montana agates contain dendrites, or tree-like plumes of mineral inclusions. (more about inclusions in Montana agate)
Finding Montana Agate
Montana agates are found over a broad area along the Yellowstone River valley and adjacent plateau areas from Emigrant MT to the North Dakota border. Rough Montana agate often resembles a potato, and is difficult to distinguish from other rocks. In the plateau areas, Montana agates may have developed a distinctive white crust, although the agates that are found away from the Yellowstone River are often more cracked and checked than the rocks that are found along the river.
Most people start collecting Montana agate by breaking likely-looking rocks with a hammer in order to learn to identify Montana agate….. experienced collectors try to avoid hammering the rocks in order to avoid ruining a potentially beautiful specimen.
Grades of Montana Agate
Back at home, the best way to evaluate Montana agate is under a strong light. Wetting the specimens may also help to show off the interior.
The finest Montana agate has a clear matrix with well-defined orange-red and black inclusions that form bands, specks, trees, or other shapes. Unchecked rock is more desirable for jewelry-making than rock that is checked or fractured. Tom Harmon of Crane, MT has published an excellent book that classifies Montana agate according to some descriptive categories.
Brief discussion of geochemistry
Montana agate is made of silica (SiO2), and the attractive inclusions consist of iron, manganese, and other minerals. The formation of Montana agate is intimately related to the occurrence of silica and color-producing minerals in Montana's past.
Volcanic material (lava flows, ash, etc.) is a common source of silica for agate formation. The silica content of lava ranges from relatively-low (basaltic lava) to relatively-high (rhyolitic lava). Rhyolite lava is thicker (more viscous) than basalt lava, and rhyolite volcanoes (such as Mount St. Helens) may be much more explosive than basaltic volcanoes (such as Kilauea on the island of Hawaii). Much of the volcanic activity in Montana and the super-massive, explosive Yellowstone volcanoes were rhyolitic, or high in silica content.
Silica is slightly soluble in groundwater at ambient temperature and pressure conditions. If silica is present in intact, relatively unfractured rock, then the rate of dissolution of silica from the rock will probably be relatively low. Much of the Montana-Yellowstone volcanism was of the explosive, rhyolitic variety, and resulted in the deposition of fine volcanic ash over extensive land areas. Volcanic ash has a high ratio of surface area to weight and, as a result, volcanic ash can react very readily with circulating groundwater to liberate silica and other minerals.
Finally, small changes in temperature, pressure, and/or micro-scale geochemistry can cause silica (and other minerals) dissolved in groundwater to precipitate out of solution. Agate is porous and may contain an appreciable amount of water ..... when precipitation of minerals occurs within an evolving Montana agate, the result may be colorful inclusions or else "healing" of cracks in the agate matrix.
Historically, Agate has been discovered with the artifacts of Neolithic people, and was used as healing amulets and ornamentation dating back to Babylon. Its medicinal uses continued through the ancient Greek and Egyptian civilizations, and spread throughout Africa and the Middle East into Russia. Agate sparked a world renowned stonecutting and polishing industry in Germany that flourished from the 15th to the 19th century, and exists today. [Simmons, 6][Mella, 67-68]
Metaphysically, Agate has a lower intensity and vibrates to a slower frequency than other stones, but is highly regarded as a stabilizing and strengthening influence. [Simmons, 6] Fiery Agates, like Laguna Agate, provide a steady, vibrant energy that stimulates a zest for living. They awaken the lower chakras and light the inner fires of Life Force, creativity, and sexuality.
Uses in industry and art
The "Rubens Vase" (Byzantine Empire). Carved in high relief from a single piece of agate, this extraordinary vase was most likely created in an imperial workshop for a Byzantine emperor.
Industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish and resistance to chemical attack. It has traditionally been used to make knife-edge bearings for laboratory balances and precision pendulums, and sometimes to make mortars and pestles to crush and mix chemicals. It has also been used for centuries for leather burnishing tools.
The decorative arts use it to make ornaments such as pins, brooches or other types of jewellery, paper knives, inkstands, marbles and seals. Agate is also still used today for decorative displays, cabochons, beads, carvings and Intarsia art as well as face-polished and tumble-polished specimens of varying size and origin. Idar-Oberstein was one of the centers which made use of agate on an industrial scale. Where in the beginning locally found agates were used to make all types of objects for the European market, this became a globalized business around the turn of the 20th century: Idar-Oberstein imported large quantities of agate from Brazil, as ship's ballast. Making use of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe. Agates have long been used in arts and crafts. The sanctuary of a Presbyterian church in Yachats, Oregon, has six windows with panes made of agates collected from the local beaches.
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