fluorescent minerals

I had an opportunity to travel to Philadelphia at the end of last week on business, and I found it an opportune time to travel north a bit on Saturday to Franklin, New Jersey to one of my favorite places . . . the Franklin Mineral Museum and the fluorescent mineral collecting site directly behind the museum. This was my fourth trip to Franklin and I enjoy it more each time. I was looking for flourescent minerals and I sure found a load of them on Saturday. I just happened to be there on the first day of the collecting season. A week earlier and I would have found the site under snow.

The first rock that I spotted looked different to me. I didn't recall having seen one like it there before, so I held on to it and kept moving it to the top of my bucket each time I placed another rock in the pile to be sorted. My first rock turned out to be a combination of willemite, zincite and franklinite. When I placed it under the short-wave UV light, it fluoresced a bright blue. It is really stunning. I also found several red willemite and several green willemite specimens. I found a piece or two of barite, there were several specimens with just a tinge of yellow fluorescence and one or two with specs of beige. And of course, there was "tons" of calcite brilliantly glowing orange. I have always found the combination of calcite and franklinite to be an attractive-looking specimen. The pictures above are red willemite from my Franklin excursion. The top one in under fluorescent light. The bottom one is under short-wave UV light.

Now just a few words about fluorescence.
Fluorescence is a property not found in all minerals. Minerals that do fluoresce, glow when exposed to either short-wave or long-wave ultraviolet light. Examples of fluorescent minerals are autinite, calcite, diamond, eucryptite, fluorite, hyalite, scheelite and willemite. Minerals from the Franklin and Sterling Hill area of New Jersey are known for their fluorescence. There are over 80 fluorescent minerals found in that area. Franklin/Sterling Hill fluorescent specimens usually contain 2-4 minerals in a typical specimen though some have up to 7 fluorescent minerals found together.

Fluorescent minerals contain particles in their structure which respond to ultraviolet light by giving off a visible glow. Ultraviolet light is a form of electromagnetic radiation invisible to the human eye. It is given off by the sun and by common fluorescent lamps used for lighting, but they also give off considerable white light (visible light), preventing the fluorescence from being seen. The ultraviolet reaction is visible with a special fluorescent lamp with a filter that blocks white light but allows ultraviolet light to pass through. This lamp is known as an ultraviolet fluorescent lamp, or UV lamp. The reaction will only be visible in a dark area, where the presence of white light is weak.

There are two ultraviolet wavelengths: long-wave and short-wave. Some minerals fluoresce the same color in both wavelengths, others fluoresce in only one wavelength, and yet others fluoresce different colors in different wavelengths. Some UV lamps have two separate filters: one for long-wave and the other for short-wave. There are more minerals which fluoresce in short-wave than there are in long-wave.

Color and intensity of the fluorescence varies among specimens of a particular mineral. However, specimens from the same locality almost always fluoresce the same color. For example, calcite may fluoresce red, orange, yellow, white or green.

When a fluorescent lamp is lit, never look at the light source, as it can damage the eyes permanently. In addition, skin should not be exposed to the light source for extended periods, as it can cause sunburns and long term skin problems.

If you have a question about fluorescent minerals, if you have additional information to add to this post about fluorescent minerals, or if you have a question or comment about another subject, please click the comment link below.


tennessee geology

Here is a look at Tennessee physical geography beginning with the eastmost region and moving westward to the Mississippi River.

Unaka Mountains: The bedrock here consists of a variety of igneous and metamorphic rocks, and is quite resistant to erosion. Due to the resistance of these rocks to erosion, and uplift associated with the mountain-making processes of the past, and the isostasy (equilibrium in the earth's crust such that the forces tending to elevate landmasses balance the forces tending to depress landmasses) of this area, the elevation throughout this area is generally 1000's of feet above sea level.

Valley and Ridge: This area consists of a large number of thrust-faulted layers or thrust sheets of rock dipping to the east at low angles. Imagine a deck of cards lying in a neat pile on a table. Now imagine a dealer spreading those cards out so that the stack is now splayed out over a much larger surface area of the table top. That should give you some idea of the nature of these thrust sheets -- except that each is several hundred to thousands of feet thick. Because the sheets dip shallowly to the east, their edges are exposed at the surface as a series of linear outcrops that are roughly oriented north to south. These thrust sheets were created as a result of continental convergence (mountain building).

Outcrops that contain mostly resistant rocks (such as sandstone or siltstone) form ridges. Outcrops that consist primarily of less resistant rocks (such as limestone or soft shale) form valleys. The result of this arrangement on a large scale is a series of north-south oriented ridges and valleys. Superimposed on these thrust sheets are smaller scale anticlines (folds with strata sloping downward on both sides from a common crest) and synclines (folds in rock in which the rock layers dip inward from both sides toward the axis) that complicate the geology somewhat. Elevations are highly variable, but generally 100's to a couple thousand feet lower than those in the Unaka's.

Cumberland Plateau: Structural geology played an important role in the development of this area. Continental convergence triggered mountain making in the Unakas and thrust faulting in the Valley and Ridge during the development of Pangaea. Much of the bedrock of this area is weather resistant, flat-lying, hardened sandstone. The resulting landscape is a tableland, or plateau, with typical elevations of 1200 to 2000 feet above sea level. These elevations are equal to, or higher than, those of the Valley and Ridge. This plateau is capped by a thick, nearly continuous sheet of resistant sandstone.

Eastern Highland Rim, Central Basin, and Western Highland Rim: Uplift of the Nashville Dome accompanied each mountain building episode in Tennessee. As a result, the regions of the Eastern and Western Highland Rims and the Central Basin all experienced periodic increases in surface elevation during the Paleozoic and early Mesozoic. At one time, the sandstones of the Cumberland Plateau probably extended westward over these areas as well. Fractures, resulting from uplift along the crest of the Nashville Dome, however, made the sandstones and the underlying limestones more susceptible to erosion. Consequently, the only remnants of these sandstones in Middle Tennessee are preserved in features such as Short Mountain. Isolated, resistant bedrock features like Short Mountain are termed erosional remnants.

Elsewhere in the Eastern Highland Rim, erosion has exposed carbonate bedrock of Late Paleozoic age. These carbonate rocks contain variable amounts of chert, and are often interbedded with fine grained, fragmented (clastic) rocks. As a result, these rocks are more resistant to erosion than the underlying, purer limestones of the Lower (Early) Paleozoic. Therefore, the Eastern Highland Rim stands above the Central Basin where Lower Paleozoic limestones crop out and erode rapidly. Structural fracturing would have been most intense over the top of the dome; therefore, the Central Basin is more deeply eroded than the adjacent Highland Rims. The geologic characteristics of the Western Highland Rim closely parallel those of the Eastern Highland Rim, resulting in very similar physical geography as well. Elevations in the Highlands Rims typically range from 600 to 1200 feet. Within the Central Basin, the elevation rarely exceeds 800 feet, with 500 to 600 foot elevations more typical.

Mississippi Embayment/Coastal Plain: The Coastal Plain is the western-most physical geographic area in Tennessee. This geographic region roughly corresponds with that of the Mississippi Embayment. In other words, the Coastal Plain was once covered by a shallow sea; when that sea regressed southward, this area became a low relief coastal plain for a while. This sea deposited numerous, flat-lying sequences of sand, silt, and mud, lying between beds of strata which together form a thick blanket of sediment. This blanket is draped over a much older carbonate bedrock surface consisting of Lower Paleozoic carbonate rock.

These relatively young marine fragmented sediments have never been deeply buried, and so are not very hard. As a result, they do not resist erosion very effectively. Instead they form a subdued, low elevation, low relief landscape, consisting of rolling hills, poorly drained lowlands, and shallow, wide stream valleys. Elevations are usually less than 500 feet and decrease rather steadily toward the Mississippi River. Recent (i.e. geologically very young) terrestrial deposits, which are simply reworked marine sediments, are slowly accumulating in many lakes and streams.

If you would like to contribute information on Tennessee geology, or if you have a question about Tennessee geology, please leave a comment to this post.


foraminifera: an amoeba with a shell

from guest contributor Howard Allen . . .

I LOVE forams! Their biggest appeal to me is their stunning diversity of forms. The smallest ones are dust-particle sized, while the largest can be nearly the size of a frisbee (see Guiness Book of Records under "largest protozoan"). A more typical size is like a grain of sand.

You can think of foraminifera (forams for short) as "an amoeba with a shell". They are classified on the basis of the composition and structure of their shells. One group has shells made up of particles of silt or sand that are glued together by the foram animal. Some of these little guys can even select particular mineral types from the sediment to make their shells: magnetite, quartz, mica, diatom shells, sponge spicules, etc. How 'bout that for a single-celled organism! Another group makes its shells of opaque white calcite that looks for all the world like fine bone china. Another group uses transparent (sometimes colored) calcite that looks like glass.

The diversity of shell shapes is mind-boggling. One critter, Lagena, has a shell that looks like an elegant, fluted glass bottle or vase. Some look like miniature ammonites. Some look like bunches of grapes. Some look like strings of beads. Some look like bananas with ribs. Some form straight tubes. Some have multiple chambers inserted at precise angles. Some look like stars. Some look like rice grains. Some look like lentils. Some are attached to the sea-bottom like little trees. The variety is endless.

The geological range of forams is very long. The oldest ones are (I think) Ordovician, and they are very common in today's seas. They are almost exclusively marine (sea water), but some are tolerant of or prefer higher or lower salinities. They are also sensitive to water temperature, depth, energy level (calm water, pounding surf).

The only real limiting factor in collecting them is that you need a microscope, preferably a binocular dissecting scope, with magnification in the range of 10x to 50x. Many of these are available for a few hundred dollars or even less for used 'scopes.

You can find forams in all sorts of sediment. The easiest way is to simply grab a vial of sand from an ocean beach and look at it under the microscope. Tropical beaches, especially those near coral reefs (Florida, Caribbean, Mexico, South Pacific islands), tend to have more and larger forams than cooler water beaches, and muddier sediment tends to have more forams than coarser sand sediment. Bermuda's famous pink sand beaches are colored by billions of red and pink forams. Planktonic (floating) forams can be collected by dragging a very fine net behind a boat. I have obtained wonderfully rich collections of forams from gobs of mud brought up on a ship's anchor in the Arctic Ocean. I ask my friends (especially those who snorkel or scuba dive) to bring me back pill bottles or film cans or small zip-lock bags with sediment from their holidays. One person brought me a bottle of sediment from the Egyptian pyramid of Cheops that was full of fossil forams (Eocene). Turns out that the pyramids were built of limestone that is chock-full of big, lentil-shaped forams. I have rice-grain sized Pennsylvanian-age forams (fusulinids) weathered loose from limestone in Texas. I have collected similar, Permian-aged forams in the mountains of central British Columbia. Chalk and marl beds are a great source of foram fossils. I have seen beautiful forams in rock cuttings from deep in oil and gas wells I've worked on in Canada and Costa Rica.

Google "foraminifera" to find photos and more information on the web. The "bible" for foram enthusiasts is Part C (2 volumes) of the Treatise On Invertebrate Paleontology, which is available at bigger libraries (especially university libraries). Have fun!


geologist offers answers

The editor of the Alberta (Canada) Palaeontological Society's newsletter, and professional geologist in the Canadian oil and gas industry has graciously offered to field questions you might have in the areas of sedimentary rocks and palaeontology. Howard has spent much time hunting dinosaur fossils, but his primary interests are invertebrate fossils and microfossils (especially foraminifera).

Howard also offers MAGS greetings and the best of luck on the launching of this blog.

I have a few questions for you already Howard. I know that foraminifera are small, single-celled organisms, of which many look like little grains of rice. Can you tell us a bit more about foraminifera? How old are they--do most of them come from the eocene? Were they ocean dwellers or shallow sea dwellers? How and where do you hunt for this particular type of microfossil?

Blog users--if you have a question that you would like to ask about invertebrate fossils or microfossils, or if you have information in this area that you would like to share with us, please click the comment link below.


geodes: how do I open them?

Opening geodes is always a lot of fun. You never know what is inside until it is open, therefore, in order to get the most enjoyment out of your geodes, you have to crack them open. There are a few ways to do that:

[01] Professional geode crackers use a set of two hardened steel points fastened to a power press, which allows you to apply pressure on the geode from two points at the same time. This is a great way to open a geode, but it is a little bit expensive.

[02] The method I prefer to use is a plumber's pipe-cutting tool. These can be found for sale on the internet and through plumbing supply houses. To open a geode using this method: find the most logical fissure or wrinkle along the outside of the geode; lock the geode in the plumber's tool and apply slow, even pressure to the handle. The geode will almost always open with a nice, even crack (no jaggies).

[03] One method is to score the geode all the way around rather deeply with a trim saw. Do this by raising the splashguard and rotating the geode by hand until it is cut all the way around. Now you can use a screwdriver to pry the two sections of the geode apart.

[04] The most common method is to lay the geode in a soft (earth) depression. Look the geode over for any cracks, weak spots, or lines that look like they might be good places to crack it open. That' where you need to apply pressure. When you have found the ideal spot on the geode, use a medium weight hammer (or rubber mallet) and center punch (NOT A STEEL CHISEL). Put the punch in a spot most likely to keep if from sliding off, and hit it several times; easy at first, then harder. If three or four blows do not open the geode, repeat in other spots until a crack does appear. Then use a screwdriver to pry your geode apart.

No matter what method you use, always use gloves and safety glasses. After you have cracked your geode, put the halves back together and secure them together with tape or rubber bands until you get them home. Never hit geodes with a hammer! Although you have on safety glasses, chips from the geode will fly in all directions, placing everyone around you in danger, and leaving chips of the brokern geode strewn all over the ground. Don't open the geodes in the field . . . take them home or to your shop or to someone who can open them for you . . . and leave the property from which you collected the geodes in just as good or better condition than it was when you arrived.

If you have additional information about geodes, unique or interesting ways to open them, or information on geode collecting sites, please leave a comment to this post.