Lake Superior Agates Field Guide (Rocks & Minerals Identification Guides)

Dan R. Lynch has a degree in graphic design with emphasis on photography from the University of Minnesota Duluth. But before his love of the arts came a passion for rocks and minerals, developed during his lifetime growing up in his parents’ rock shop in Two Harbors, Minnesota. Combining the two aspects of his life seemed a natural choice and he enjoys researching, writing about, and taking photographs of rocks and minerals. Working with his father, Bob Lynch, a respected veteran of Lake Superior’s agate-collecting community, Dan spearheads their series of rock and mineral field guides―definitive guidebooks that help amateurs “decode” the complexities of geology and mineralogy. He also takes special care to ensure that his photographs compliment the text and always represent each rock or mineral exactly as it appears in person. He currently works as a writer and photographer in Madison, Wisconsin, with his beautiful wife, Julie. Bob Lynch is a lapidary and jeweler living and working in Two Harbors, Minnesota. He has been cutting and polishing rocks and minerals since 1973, when he desired more variation in gemstones for his work with jewelry. When he moved from Douglas, Arizona, to Two Harbors in 1982, his eyes were opened to Lake Superior’s entirely new world of minerals. In 1992, Bob and his wife Nancy, whom he taught the art of jewelry making, acquired Agate City Rock Shop, a family business founded by Nancy’s grandfather, Art Rafn, in 1962. Since the shop’s revitalization, Bob has made a name for himself as a highly acclaimed agate polisher and as an expert resource for curious collectors seeking advice. Now, the two jewelers keep Agate City Rocks and Gifts open year-round and are the leading source for Lake Superior agates, with more on display and for sale than any other shop in the country.

Floater Agate

Synonyms: Floater, suspended-center agate, suspended-banding agate

Characteristic features: Regions of chalcedony banding surrounded by thick bands of coarse quartz crystals; a single region of chalcedony banding surrounded by quartz may exist at the center of a specimen, or banded chalcedony sections may alternate with layers of coarse quartz crystals

Rarity: Floater agates are fairly common in the entire Lake Superior region, but are not quite as abundant as fortification agates

Description: While the name “floater agate” was invented by collectors and is not a scientific term, there is no better way to describe the “islands” of banded chalcedony that seem to float in masses of quartz in these agates. While they all contain ample amounts of chalcedony and quartz, there are two types of floater agates. Some consist of a single central mass of chalcedony surrounded by one body of quartz, while others consist of alternating regions of banded chalcedony and quartz, creating several “floating” bands. As chalcedony requires much more silica to form than macrocrystalline quartz, the varying amounts of each in a floater agate reflect dramatic rises and falls in the amount of available silica during the agate’s formation. These wild swings in silica content led to the formation of large individual quartz crystals within the macrocrystalline quartz, creating jagged boundaries between the chalcedony and quartz layers. When the chalcedony resumed forming, it filled in around these crystal points, preserving their shapes. These unique jagged borders are found in almost all specimens

Identification: Floater agates are a variation of fortification agates (page 23), and as such they contain the common band-within-a-band agate structure. But unlike classic fortification agates, some of the bands within floaters are composed entirely of coarse macrocrystalline quartz. This is the first thing to look for when identifying these agates. The macrocrystalline quartz is always evident in both floater agate types, and the quartz layers are typically quite thick and noticeably more plentiful in floater agates than in fortification agates. The banded quartz agate (page 41) is the only agate type you’re likely to easily mistake for a floater agate, but that’s only likely if a specimen is nearly whole and doesn’t show much of its interior pattern. Banded quartz agates contain little to no interior chalcedony banding and instead exhibit a large central mass of macrocrystalline quartz, so if only a small, shallow portion of an agate’s interior is visible and only macrocrystalline quartz can be seen, it could be a banded quartz agate, or it could be a floater agate with the chalcedony bands hidden deeper within. If there are few other clues, only cutting the agate will reveal its identity.

Collectibility: Normally just called “floaters” by collectors, floater agates are often visually interesting and can be very collectible when colorful. But as with any variety of Lake Superior agate, many collectors dislike floaters that contain excessive amounts of macrocrystalline quartz. However, with the right balance of chalcedony banding, macrocrystalline quartz thickness, and vivid coloration, floaters can be very desirable and valuable.

Compare & Contrast:

Banded Quartz Agate: more quartz and less chalcedony banding

Agate Geode: Can exhibit quartz bands, but has a hollow center

Fortification Agate: No large quartz bands

Skip-an-Atom Agate: Quartz bands are opaque and grayish blue

Where to begin looking: As one of the most common types of agate, floaters can be found anywhere in the region. Gravel pits near Cloquet, Minnesota, are very lucrative, as is Ontario’s Lake Superior shoreline.

Details

• Publisher ‏ : ‎ Adventure Publications (May 22, 2012)
• Language ‏ : ‎ English
• Paperback ‏ : ‎ 161 pages
• ISBN-10 ‏ : ‎ 1591932823
• ISBN-13 ‏ : ‎ 978-1591932826
• Item Weight ‏ : ‎ 5.6 ounces
• Dimensions ‏ : ‎ 4.3 x 0.2 x 5.9 inches