FMF - Friends of Minerals Forum, discussion and message board

[Bob Harman]

More examples of dolomite from different Indiana localities. These examples are from Indiana geodes. You can see the wide range of colors and hues....pink thru all shades of orange to brick red. This seems due to iron oxides and several color shades often occur side by side in the same geode. Careful observation reveals subtle differences in the dolomite crystal sizes. The example shown above from Corydon Quarry shows much larger pink dolomite rhombs than the geode examples and the Harrodsburg examples are often slightly larger than those dolomite crystals found in examples from the Washington County road cut locality.

[Bob Harman]

Back in the 1960s (maybe even earlier) thru the early 1970s the Meshberger Stone Quarry near Columbus, Indiana (actually nearer the small town of Elizabethtown, Indiana) produced many large and very hi quality calcites. I have personally seen 15 cm perfectly doubly terminated crystals. But nothing has come out of that quarry since before 1980. The management of this quarry is the epitome of bad relations between quarry management and the collector community. I am told by very good sources that even inspectors must stay in their vehicles when doing their various inspections and duties in the quarry! My 10 cm example was collected about 1967.

[Bob Harman]

Here are several pix of another Indiana collecting locality. The rocky banks of a southern Indiana lake. The limestone at this site might be more correctly be called a sandy siltstone. The geodes at and near this site include many with aragonite and my smoky quartz examples. These pix are from the spring of 2012. The only time hiking on the lake is successful is after long dry spells when the water level is low. After rainy spells, mostly in the spring, the lake levels are high and there are no beaches as the water goes back into the wooded areas. Right now, in May of 2016, the water level on area lakes is still quite high but beginning to fall.

[Bob Harman]

As I mentioned above with my Corydon Crushed Stone Quarry dolomite examples, fluorite is often found in small crystals in that quarry. Here are the most usual expressions of that mineral. There are rare yellow cubes up to about 1 cm upon pink dolomite as seen on the right side specimen. Then there are somewhat more common purple cubes associated with the pink dolomite and also calcite. These can also be up to about 1 cm in size.
The most interesting expression tho is seen on the left side example. Congruous tiny 1mm cubes fill small voids in the host dolostone. Upon casual looks, the areas appear as ink well like depressions filled with old time dark purple fountain pen ink. Sometimes many of these occur in a localized area of the host rock making for a rather aesthetic overall appearance.

These examples were collected about 2000.

[Bob Harman]

The Indiana rte 56 roadcuts in Washington County, East of the town of Salem Indiana host some of the most colorful, highest quality, and most collectible geodes in Indiana. Many can have their best areas culled out from the geodes, making nice quality non-geode specimens.
The host matrix is very porous dolostone absorbing large amounts of water and then splitting and fracturing very readily in freeze/thaw episodes. In late winter and spring rockfalls are common and can be dangerous to careless collectors. Unfortunately many very hi quality specimens are lost to breakage as the rock wall splits, fractures and falls into many pieces before the examples are freed up and collected. My locality pix show the roadcut in winter and summer including a large hi quality geode containing large calcites on bright red dolomite. Unfortunately, it is fracturing. This pix was from 2012; the geode is now history.

[Bob Harman]

As previously mentioned, pyrite is found in many Indiana localities. Shown here are 2 varieties from a little known locality, the Georgia Quarry, West of the town of Mitchell in Lawrence County. This is the same quarry that the selenite and satin spar varieties of gypsum was pictured.
The pyrite here occurs as striated silvery cubes up to 1 cm. Occasionally many cubes can be found in close proximity in the limestone matrix which can easily be etched away with vinegar or dilute hydrochloric acid. The pyrite also replaces invertebrate fossils, a shell as shown here.

[Bob Harman]

Many dedicated field collectors, over a long period of time, find very small and localized localities. These localities produce a few specimens and then are often played out. Only 1 or a very few collectors own specimens from these finds. So it has been with me.
The 2 pix show 2 of about 10 total examples from such a locality. In about 2007, during the building of a new housing subdivision South of the city of Bloomington, heavy equipment got into geode bearing limestone while excavating a small 1 acre storm water retention pond. This was relayed to me and over the weekend I walked back and forth thru the broken up rock, finding about 10 collectible examples. One I gave to a collector friend, one I, regretfully, sold and the remainder are still in my collection. After that weekend, the site was contoured and covered over with gravel. Today it is an extinct locality under a housing subdivision and small storm water pond. Ten total specimens owned by 3 people.

[Bob Harman]

Perhaps these 2 maps should have been added to this thread at the very beginning. The map of the USA shows many of the geode locations where collector quality examples can be found. I do not profess that it is nearly complete or totally accurate, but it does give a sense of orientation when asking about field collecting geodes from the USA. Most importantly, it shows the large area of Midwest sedimentary geode locations. The Keokuk geode area in Southeast Iowa and nearby. The Eastern Missouri and Illinois areas and my Indiana area from South-central Indiana southward thru Central Kentucky into a few areas of Tennessee.

The Indiana map hi lights the area of the South-Central part of the state where mid Missippian age rock comes to and near the surface with its geode producing layers. This area is within the red line and only comprises several counties.

[Bob Harman]

There are several close but distinctly different Baryte producing localities in southern Monroe County Indiana. By far the most well known is the Harrodsburg roadcuts locality, but just a mile or two away are the Monroe Reservoir spillway locality and the virtually unknown Mission Valley Ravine locality. These 2 geodes are from the Mission Valley locality. This site has produced a few large, stout and often hi quality Baryte crystals as seen here. Fresh and well displayed examples are sought after by many mineral dealers familiar with Midwest minerals and geodes.

[Bob Harman]

Hunting for nice quality collectible quartz geodes in Indiana is a favorite family pastime and, perhaps the most important aspect of American Midwest geodes, is that it is a common gateway for many youngsters into the world of fossil and mineral collecting and geology in general.
Microcrystalline quartz (chalcedony) geodes are common, but not nearly so common as ordinary quartz geodes. Many botryoidal forms may be found including many aesthetically stained with iron oxides. As many are found already broken and open as are found as whole geodes. All these examples are from Monroe County Indiana.

[Bob Harman]

Monroe Reservoir, more commonly known as Lake Monroe or Monroe Lake, is a reservoir built by the U.S. Army Corps of Engineers in 1964. It is the water supply for Bloomington Indiana and several nearby smaller communities. It dams up Salt Creek and is used for flood control in southern Indiana. Its normal level (pool level) is 538 feet (above sea level) and the spillway, used as a parking lot and recreational entry to the lake is 552 feet. Two times since 1964 has the spillway been overrun by high water.
The spillway was cut out of a limestone ridge that runs along a portion of the Lake's South shore. The spillway cut is about 75 feet high on both sides and about the width of a U.S. football field. Local collectors can, with some effort, get to several levels hi up on the spillway rock walls to hunt geodes and fossils. These are 5 pix of 3 examples.
These geodes commonly have thin transparent and lustrous pale yellow terminated Baryte along with peculiar frosty calcites. Dolomite and other minerals are very rare. Since the geodes are removed from surrounding limestone which has only recently become exposed, they are usually quite fresh and bright.

[GneissWare]

Very nice Bob!

[Bob Harman]

In 2013, while field collecting at the Indiana rte 56 road cuts in Washington County, a fellow pulled off the road near my collecting. When this happens, I get a little anxious as to what the stranger's motives might be. This fellow though, was a friendly local who was interested in what I was doing and proceeded to tell me that he lived nearby with considerable surrounding land. He had a stream in a ravine and had seen geodes in it and said, if I wanted, I could explore the area. In general going onto private property is no so easy here in the U.S. Midwest, but I thanked him.
The next time I was down there, I made it a point to seek out his ravine with not much real hope as these situations rarely lead to anything substantial. The site was a steep heavily wooded rocky ravine with a sharp bend and a shallow stream coursing thru the ravine. The rocky walls of the ravine actually hosted a few large and very large promising geodes so I became rather enthused. The whole site is not very big and over these past 2 years I have found about a dozen very collectible and hi end examples. These 2 pictured are probably the 2 best examples. The very large example has been shown to several dealers at the larger shows and they suggest culling out the area with the calcites to make a specimen rather than a geode, but so far, I have resisted.

[Bob Harman]

An extremely unusual occurrence is this hyalite opal on the crystal tips of otherwise rather ordinary quartz. Of my 2 examples, this is the better one. I have never seen any others.
Defined as a colorless rather amorphous glass like silica or quartz with about 3% - 5% water, this form of quartz may be widely found, but apparently not, as far as I know, in Indiana geodes.

[Jamison Brizendine]

Bob, does the hyalite fluoresce like the Mexican and African hyalite?