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Agate is a microcrystalline variety of quartz (silica), 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 but can be common in certain metamorphic rocks.
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, sometime between the 4th and 3rd centuries BC.
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.
Most agates occur as nodules(a small knobbly rock or mineral cluster) in volcanic rocks or ancient lavas where they represent cavities originally produced by the disengagement of volatiles in the molten mass which were then filled, wholly or partially, by siliceous(containing, resembling, relating to, or consisting of silica.) matter deposited in regular layers upon the walls. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity(lack of thickness, density, or substance.), giving a banded appearance to the section. Such stones are known as banded agate, riband agate and striped agate.
Types of Agates:
A Mexican agate, showing only a single eye, has received the name of cyclops agate. Included matter of a green, golden, red, black or other color or combinations embedded in the chalcedony and disposed in filaments and other forms suggestive of vegetable growth, gives rise a moss agate.
Dendritic agates have fern like patterns in them formed due to the presence of manganese and iron oxides. Other types of included matter deposited during agate-building include sagenitic growths (radial mineral crystals) and chunks of entrapped detritus (such as sand, ash, or mud). Occasionally agate fills a void left by decomposed vegetative material such as a tree limb or root and is called limb cast agate due to its appearance.
Turritella agate is formed from silicified fossil Elimia tenera (erroneously considered Turritella) shells. E. tenera are spiral marine gastropods having elongated, spiral shells composed of many whorls. Similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey stone or agate.
Greek agate is a name given to pale white to tan colored agate found in Sicily back to 400 B.C. The Greeks used it for making jewelry and beads. Today any agate of this color from Sicily, once an ancient Greek colony, is called Greek agate. Yet the stone had been around centuries before that and was known to both the Sumerians and the Egyptians, who used the gem for decoration and religious ceremony.
Another type of agate is Brazilian agate, which is found as sizable geodes of layered nodules. These occur in brownish tones interlayered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.
Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due to the extreme delicacy of the successive bands, whence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process.
Other forms of agate include Lake Superior agate, carnelian agate (usually exhibiting reddish hues), Botswana agate, Ellensburg blue agate, blue lace agate, plume agates, tube agate (with visible flow channels), fortification agate (which exhibit little or no layered structure), fire agate (which seems to glow internally like an opal) and Mexican crazy-lace agate (which exhibits an often brightly colored, complex banded pattern) also called Rodeo Agate and Rosetta Stone depending on who owned the mine at the time.
Many agates are hollow, since deposition has not proceeded far enough to fill the cavity, and in such cases the last deposit commonly consists of quartz, often amethyst, having the apices of the crystals directed towards the free space so as to form a crystal-lined cavity, or geode.
At this well-known agate beach, you might find the variegated, translucent stones of quartz while strolling along the shoreline looking through the clear water, especially in spring or after a storm.
Requirements:
Please e-mail me the answers, do not post them in your log.
#1. What type of agate would you find at the posted coordinates? (If you read the cache page, this should be an easy one.)
#2. Lake Superior Agates are typically red, orange, and yellow in color. Look around you. Based on the color of the majority of the rocks on this beach, are agates a common or rare find? Why?
#3. What man-made thing is built at the posted coordinates?
#4. Did you find any Agates while you were here?
#5. Optional- post a picture of your GPS with the man-made structure and the lake in the picture. you may take the picture with you or part of your team with GPS in hand with the lake behind you.
If you don't find any agates, or you really want to see some cool looking agates, youi may want to visit gitche gumee agate and history museum. coords are:
N46 40.362 W85 59.204
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