1. Go to a peridotite exposure.
2. At the site, study the characteristics of the exposure. Note how much is weathered and how much is relatively fresh.Note the color and texture of the weathered surface, and of the relatively fresh rock, if visible. Note the extent of alteration (serpentinization, etc.), if any.
3. Collect hand samples. Try to get at least a few samples from outcrops, and write down where you got them.
4. Break some of the hand samples to expose fresh surfaces (This can be done later). Examine both the fresh surfaces and the weathered surfaces with a hand lens. Note the color and texture. Crush a small piece of the rock with a hammer, and examine the fragments with a hand lens. Note the shapes of the individual grains, and, if possible, the characteristics of crystals, if any. Don't overlook the tiniest crushed grains - they can be the most interesting. Put some of the fragments in a small container and take them home to look at under a microscope (in ordinary light).
5. If you have a rock saw at home or in a lab, cut flat surfaces on some of the samples.
6. If you have a slab polisher, polish some of the cut surfaces to better see the internal structure of the rock. Study the polished surfaces with a hand lens. Can you see the grain boundaries in the rock? Can you distinguish olivine from pyroxene? If you don't have a polisher, you can get a pretty smooth surface with silicon carbide paper. That's what I do. It's tedious and time consuming, but it works.
7. Send some small samples out to have thin sections made. It will cost between $20 and $30 per thin section. It's sometimes cheaper if you cut the samples to size yourself, about 14x25x45 millimeters, before you send them to the thin section shop. This also has the advantage of allowing you to specify exactly what gets in the thin section.
8. Study the thin sections under a polarizing microscope, and photograph features of interest. You'll see a lot of things when you look at the photomicrographs that you missed looking through the microscope. If you don't have a polarizing microscope, see "About this Blog". There's a picture and description of a homemade one that will cost less than $350, including a camera adapter (but not the camera). You can also photograph the thin sections in cross-polarized light without a microscope. Sandwich a thin section between two polarizing filters and put it on a light box. Then take a macrophotograph of it. There are several of them on this blog.
HOWEVER, If you can't do the above, there is a great variety of pictures on the Web. Although peridotites aren't always evident at the landscape scale, some of them are, as shown below:
LANDSCAPE SCALE:
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| Google Earth image of Bay of Islands area, Newfoundland, Canada. Large peridotite exposures (light-colored areas) from lower left to upper right: Lewis hills, Blow-Me-Down Mountain, North Arm Mountain, Table Mountain (also known as The Tablelands). Click on image to enlarge. |
Andrew Collins' photo (below), taken on Blow-Me-Down Mountain, captures the color of weathered, serpentinized peridotite, and the barren, desert-like character of the landscape.
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| Panorama atop Blow-Me-Down Mountain by Andrew Collins via Panoramiio. Click on image to enlarge. |
OUTCROP SCALE:
Geology dept./class web sites and blogs
text
HAND SAMPLE SCALE:
Web scan
THIN SECTION SCALE:
Books:
color reproduction problems
limited examples
The Web: Photos of thin sections (photomicrographs) are not as abundant on the Web as are photos of hand samples. That's probably because, to make photomicrographs, one needs a polarizing microscope with a camera attached. Furthermore, a lot of the photomicrographs that are accessible on the Web are in scientific journal articles that require association with a library that subscribes to the journal. Even if you do have access to scientific journals, the thin sections reproduced in articles are usually very small, of low resolution, and in monochrome.
If you search for "thin sections" on Google, you'll retrieve many screens full of dazzling pictures. However, under this generic heading, the images seem to be chosen for their vivid colors, and, as in any Google "images" search, they're not labeled. You'll have to go to the site where each picture resides in order to find out what it is.
Many university geology departments or petrology/mineralogy instructors set up thin section galleries in the early days of the Web. Although many of these now require university IDs for access, others are still freely accessible. Searching for "peridotite thin sections" (without the quotes) may turn up good examples with useful text descriptions at the Web site of origin..
It's also worthwhile looking at thin sections that are for sale. Even though you're not interested in buying them, you can get a look at a variety of examples showing different features. I searched Google for "peridotite thin sections for sale" (without the quotes), and about five or six screens down, I came across this:
This thin section was listed on Ebay.UK, where it had recently sold for £24.49. With the £3 shipping charge that's about $40 US. The seller identified it as "metasomatized harzburgite" from Finero, Italy. I don't have anything exactly like this in my collection. I wouldn't mind paying that price for it if I could get the full particulars. For starters, I'd want to know the dimensions of the microscope slide, and whether this photo shows the whole thin section or only a part of it. But considering what I'd have to go through to find a specimen like this, and have a thin section made of it, $40 is cheap.
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