History’s Gem of the Month: Hints on Hunting and Finding Agates – PART II

 Fall 2009

While I was looking for something to include for this month’s history gem, I ran across yet another article written by Axel, which is different than the one that I included last month. This one is a rough draft, and required editing.

Hints on Hunting and Finding Agates
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.

Remember that rockhounds never die, they just grind away.

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