member-owned

Things from the personal rock collections of members of the Show-Me Rockhounds

Hematite Magnetite

hematite magnetite

Photo by Stephanie Reed

This hematite and magnetite specimen is from Patagonia, Argentina. Bruce got it at the Denver show and gave it to Sharon Penner. It’s about 4 inches long and pretty shiny.

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Fairburn Agates

Special guest article from Show-Me Rockhounds club members Dan and Connie Snow

Fairburn agate fortification agate

Group picture of Fairburn agates – Dan Snow

Fairburn agates are a form of microcrystalline chalcedony, 100% silicon dioxide with a hardness of 6 ½ to 7 on the Mohs scale.  They are also called fortification agates because of their banding.  They were formed approximately 300 million years ago in an ancient limestone bed of an inland sea.  To hunt Fairburn agates requires looking at every rock and turning many with a rock pick.  It is strictly surface hunting no digging, mining, cracking or breaking rocks.   The photos shown are exactly the way the agates were found, with no cutting, polishing or tumbling having been done.

Fairburn agate fortification agate

Frog Rock – Dan Snow

Fairburn Agates found by Dan and Connie Snow. Collected from the Fairburn Agate beds of South Dakota and the Oglala National Grasslands in Nebraska.

Characterization of Green Amber

silver ring with oval green amber

Green amber ring owned by Stephanie. It has nothing to do with this article. Photo by Stephanie Reed

David highly recommends this article on green amber from Gems & Gemology, 2009. Here is the abstract.

Ahmadjan Abduriyim, Hideaki Kimura, Yukihiro Yokoyama, Hiroyuki Nakazono, Masao Wakatsuki, Tadashi Shimizu, Masataka Tansho, and Shinobu Ohki

Abstract: A peridot-like bright greenish yellow to green gem material called “green amber” has recently appeared in the gem market. It is produced by treating natural resin (amber or copal) with heat and pressure in two stages in an autoclave. Differences in molecular structure between untreated amber and copal as compared to treated “green amber” were studied by FTIR and 13C NMR spectroscopy, using powdered samples. Regardless of the starting material, the FTIR spectrum of “green amber” showed an amber pattern but with a characteristic small absorption feature at 820 cm-1. Solid-state 13C NMR spectroscopy of the treated material indicated a significantly lower volatile component than in the untreated natural resin, evidence that the treatment can actually “artificially age” copal. A new absorption observed near 179 ppm in the NMR spectra of all the treated samples also separated them from their natural-color counterparts.

To read the whole article, go here http://www.gia.edu/gems-gemology/fall-2009-green-amber-abduriyim and click on “Download PDF”.

Selenite Stories

Gray selenite crystal and orange selenite crystal, both about the size of a ballpoint pen.

Photo by Stephanie Reed

Selenite is a type of gypsum that has a flat reflective surface, usually gray, clear, white, or amber. Red is an unusual color for selenite, but they do exist. It is very soft and can be scratched by a fingernail (2 on the Mohs scale). At our February meeting, two of the door prizes were these selenite crystals found by President David Reed. The amber one is from Lake Kanopolis in Kansas. The gray one is from Lake Wilson, which is also in Kansas. David went to Lake Wilson and put a small crystal in the mud. He returned 3 years later and found the large gray crystal.

One time David and Stephanie went to Kansas and found several selenite crystals somewhere near the dam at Lake Wilson. They were gray like this one pictured, but much smaller. On the April field trip to Marquette, some club members also found selenite crystals.

Spring Forward to the Show

mineral clock with agates and apache tears

Photo by Stephanie Reed

We interrupt the Spring Gem and Mineral Show to remind you to set your clock forward one hour tonight for Daylight Savings Time.

This clock is from the collection of David Reed. It contains agates, Apache tears (obsidian), a craft store clock kit, and lots of resin. It looks pretty good with his other rock clock.

Composita

Lots of Composita shell fossils found in Kansas City

Photo by Stephanie Reed

If you came to our January meeting, you will know that we are now offering door prizes just like at IGAMS. All my spying on IGAMS meetings is proving to be very helpful! January’s door prize was part of Kansas City’s Composita layer. Composita is a genus of extinct brachiopods that were abundant during the Pennsylvanian era. Brachiopods are bottom-dwelling marine organisms that have two shells[1] and a little fleshy “foot” called a pedicle. In a fossil brachiopod, you can see the hole where the pedicle sticks out of the shell, which is called the pedicle valve. In the upper part of the Winterset Limestone in Kansas City, there is a zone consisting almost entirely of Composita shells. See Chapter 11 of Dr. Gentile’s book for more information. Some of the shells in this specimen even had crystals inside. It was collected by David Reed somewhere in the Kansas City area, but he’s not telling exactly where.

[1]Brachiopods have two shells, but they are not bivalves (an easy mistake to make). Bivalves are a class of mollusks, like clams, and do not have pedicles. Bivalves are symmetrical, and brachiopods are not. In fact, the bivalves may have caused the extinction of the brachiopods due to competition for food and living space.

Angelwing Chalcedony

Article by special guest author David Reed

a long flowing wing-shaped rock appearing to be made of several small tubes, with red and blue colors.

From the collection of David Reed, photo by Stephanie Reed

This refers to a surface chalcedony formation characterized by groups of chalcedony filaments often intricately woven or connected together, so they resemble the feathers of a wing or flowing hair. They occur most often in the center of a vug or vein of agate, but can also occur in the center of a hollow thunderegg. These formations are usually found in Idaho or Oregon. It describes this type of surface chalcedony formation, regardless of whether the underlying formation is plume agate, tube agate, or moss agate. See below for several close-ups, all from the same specimen.

Close-up of red tube formations

Photo by Stephanie Reed

Close-up of blue and orange tubes

Photo by Stephanie Reed

Lots of chalcedony filaments all pointing the same way

Photo by Stephanie Reed

The tubes in Angelwing Chalcedony seem to follow the direction of flow of the silica-bearing fluid in air within the vug. They may form in similar fashion to the directional helictites (gypsum formations) in Lechugilla Cave (and elsewhere), or they may be directional helictites which were silicified.

Lechuguilla_Chandelier_Ballroom

Lechuguilla Chandelier Ballroom photo by Dave Bunnell

long squiggly white directional helictites

Directional Helictites Photo by Dave Bunnell

Although it looks similar, Angelwing Chalcedony is not the radiating tubes found in fossils of certain coral heads.  Angelwing Chalcedony was never alive, but the coral was. During mineralization, the form of the living coral was maintained, but the structure was changed from mostly calcite to mostly silica, and some of the voids were filled. The structure of the fossil is more regular; there was no irregular flow of fluid through a void, as there was with the Angelwing Chalcedony. The fossil specimen below was found eroding out of a Florida riverbed. It was purchased, to avoid diving with the alligators.

A round brown chunk of tiny tubes of coral with a white crust on the outside

From the collection of David Reed, photo by Stephanie Reed

Ironwood

A piece of ironwood seen from below

At a previous meeting, Martin Mueller showed off this piece of ironwood. Ironwood is not a rock or mineral, and although it may look similar, ironwood is not petrified wood. It is a name for many different types of wood that are said to be hard. It has a nice wood grain texture at the polished bottom. Sadly, I have forgotten what kind of wood this is and where it came from (it wasn’t from Westeros!). Does anybody know?

A piece of ironwood seen from the side.