LAKE SUPERIOR USA AGATE RED EYE CANDY DRUZY BANDED TUBE LAPIDARY STONE ROCK PILE

The Lake Superior agate is a type of agate stained by iron and found on the shores of Lake Superior. Its wide distribution and iron-rich bands of color reflect the gemstone's geologic history in Minnesota, Wisconsin, and Michigan. In 1969 the Lake Superior agate was designated by the Minnesota Legislature as the official state gemstone.

The Lake Superior agate was selected because the agate reflects many aspects of Minnesota. It was formed during lava eruptions that occurred in Minnesota about a billion years ago. The stone's predominant red color comes from iron, a major Minnesota industrial mineral found extensively throughout the Iron Range region. Finally, the Lake Superior agate can be found in many regions of Minnesota as it was distributed by glacial movement across Minnesota 10,000 to 15,000 years ago.

More than a billion years ago, the North American continent began to split apart along plate boundaries. Magma upwelled into iron-rich lava flows throughout the Midcontinent Rift System, including what is now the Minnesota Iron Range region. These flows are now exposed along the north and south shores of Lake Superior. The tectonic forces that attempted to pull the continent apart, and which left behind the lava flows, also created the Superior trough, a depressed region that became the basin of Lake Superior.

The lava flows formed the conditions for creation of Lake Superior agates. As the lava solidified, water vapor and carbon dioxide trapped within the solidified flows formed a vesicular texture (literally millions of small bubbles). Later, groundwater transported ferric iron, silica, and other dissolved minerals passed through the trapped gas vesicles. These quartz-rich groundwater solutions deposited concentric bands of fine-grained quartz called chalcedony, or embedded agates.

Over the next billion years, erosion exposed a number of the quartz-filled, banded vesicles—agates—were freed by running water and chemical disintegration of the lavas, since these vesicles were now harder than the lava rocks that contained them. The vast majority, however, remained lodged in the lava flows until the next major geologic event that changed them and Minnesota.

During the ensuing ice ages a lobe of glacial ice, the Superior lobe, moved into Minnesota through the agate-filled Superior trough. The glacier picked up surface agates and transported them south. Its crushing action and cycle of freezing and thawing at its base also freed many agates from within the lava flows and transported them, too. The advancing glacier acted like an enormous rock tumbler, abrading, fracturing, and rough-polishing the agates.

Description
The Lake Superior agate is noted for its rich red, orange, and yellow coloring. This color scheme is caused by the oxidation of iron. Iron leached from rocks provided the pigment that gives the gemstone its beautiful array of color. The concentration of iron and the amount of oxidation determine the color within or between an agate's bands. There can also be white, grey, black and tan strips of color as well.

The gemstone comes in various sizes. The gas pockets in which the agates formed were primarily small, about 1 cm in diameter. A few Lake Superior agates have been found that are 22 cm in diameter with a mass exceeding 10 kilograms. Very large agates are extremely rare.

The most common type of Lake Superior agate is the fortification agate with its eye-catching banding patterns. Each band, when traced around an exposed pattern or "face," connects with itself like the walls of a fort, hence the name fortification agate.

A common subtype of the fortification agate is the parallel-banded, onyx-fortification or water-level agate. Perfectly straight, parallel bands occur over all or part of these stones. The straight bands were produced by puddles of quartz-rich solutions that crystallized inside the gas pocket under very low fluid pressure. The parallel nature of the bands also indicates the agate's position inside the lava flow.

Probably the most popular Lake Superior agate is also one of the rarest. The highly treasured eye agate has perfectly round bands or "eyes" dotting the surface of the stone.

Cutting and polishing
A gemstone can be used as a jewel when cut and polished. Only a fraction of the Lake Superior agate are of the quality needed for lapidary. Three lapidary techniques are used on Lake Superior agates:

Tumbling—Small gemstones are rotated in drums with progressively finer polishing grit for several days until they are smooth and reflective.
Saw-cut and polish—Stones up to 1/2 kg are cut with diamond saws into thin slabs, which then are cut into various shapes. One side of the shaped slab is polished producing fine jewelry pieces and collectible gems called cabochons. (Note the value of large Lake superior agates, which weigh a few pounds or more, will lose most of their value if cut into slabs.)
Face polishing—Polishing a curved surface on a portion of the stone and leaving the major portion in its natural state is called face polishing.
Distribution of Lake Superior agate
One of the most appealing reasons for naming the Lake Superior agate as the Minnesota state gemstone is its general availability. Glacial activity spread agates throughout northeastern and central Minnesota, northwestern Wisconsin, Northern Iowa, and Michigan's Upper Peninsula in the United States and the area around Thunder Bay in Northwestern Ontario, Canada. Lake Superior agates have been found in gravel deposits along the Mississippi River basin. Other types of agate similar to Lake Superior agate have been found in southwestern Wisconsin.

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By Axel Niemi and Karen Brzys
There are two outward appearances to a Lake Superior agate. Some have the unworn outer look, while others have a worn or broken and chipped look. Most Lake Superior agates have an almond shape, called amygdaloidal. This denotes that the agate formed inside vacated gas pockets inside what was originally molten lava. As the gas gets trapped in the molten lava, the lava continues flowing, elongating the gas pocket. As the lava continues to cool, the pockets also harden, after which the steam escapes. Silicon dioxide quartz, with impurities of other minerals, later fills the pocket. The quartz and other impurities form submicroscopic crystals to fill in the pocket.

The unworn agate with original outer husk is more difficult to recognize. However, these unworn agates are usually only found where they formed, and must be mined out of the basaltic lava material. Most Lake Superior agates that have eroded out of the basalt are gravel-worn and easier to spot and recognize. All chipped agate has a waxy surface texture, which can expose the translucent nature of the microcrystalline quartz as well as the banded structure. Thus, in most cases when you are agate hunting on the beach, agates are rare but when you find them, it is usually obvious that they are agate. If you are not sure if it is an agate, it probably is not.

Several different types of agate can be found on the Lake Superior beach, some of which include:
Candy Stripe Agate: An agate with alternating red and white bands.
Carnelian Agate: A translucent agate with red to brown-red color. Carnelian can also form without banding.
Eye or Orbicular Agate: An agate with a circular eye formation on the outside of the specimen.
Fortification Agate: Agates with concentric bands.
Moss Agate: These agates have mossy looking mineral inclusions.
Paintstone or Dryhead Agate: These agates are not translucent due to the larger amount of impurities that are contained within the specimen. Many have pink and tan colors.
Peeler Agate: When agates are exposed to the weather, some of the bands may erode at a different rate than others. The result is an agate wherein the bands seem to have peeled back, like the layers of an onion.
Ruin Agate: These agates form with the pattern is broken, and then re-cemented back together by additional agate formation.
Sagenite Agate: These agates have many fine crystals, elongated and fan shaped, usually as an inclusion inside an agate. The fine crystal “needles” are usually formed by the mineral rutile.
Shadow Agate: These agates have tight banding with alternating opaque and translucent layers. As light enters the agate, it bounces between the layers. When you move the agate back and forth, you can see what appears to be a shadow, racing across the surface.
Tube Agate: In some cases, agate replaces other tube-shaped minerals forming interesting elongated patterns.
Water Level Agate: These agates have bands formed in parallel layers.

quartz
floater
dark & gnarly
red & white beauty
onyx-fortification
water-level agate
eye agate

SUPER RESOURCE
http://www.mineralworld.de/assets/applets/The_Other_Lake_Superior_Agates_2nd_edition_5-6-03.pdf