The dark images are taken in cross-polarized light using a petrographic microscope, a common tool of geologists. In this light, translucent and transparent materials with ordered crystalline structure that varies with direction (anisotropic materials such as most minerals) are bright white, gray, or colored, while isotropic materials (such as diatoms, glass, and crystalline materials with structure that is the same in all directions) are dark and nearly invisible. The birefringence colors of crystalline materials are a key mineral identification tool, and depend on the crystal structure and the thickness of the mineral grain in the slide. Most cross-polarized light images are paired with an image in plane-polarized light of the same scene.
In this age of great online resources, we prefer to delegate definitions, background information, and technical details to other experts. Wikipedia and dictionaries such as Merriam-Webster’s are excellent resources. Each mineral description in TMI includes a link to Mindat, which contains more information about the crystallography, chemistry, etymology, and occurrence of the mineral than we could ever hope to include in TMI. Similarly, diatoms are linked to Diatoms of the United States, a growing expert resource.
At the moment you have to rely on comparison with the other images of that component and identification of the commonalities, as well as the description of the component. Many users have requested that we tag components in images (in a similar way to tagging people in photos on Facebook), and we’re working on a software solution.
Where available, this information and other metadata can be seen by hovering your mouse over the image.
You can see the pollen identification (genus and usually species) by hovering your mouse over an image.
Please see “How to contribute” on the main Help page.
Yes! At least we can try.
It is much harder to ID something from an image than from an actual slide, and SEM/EDX or x-ray diffraction may help to identify the component. If possible, please send a small sample of your material so that we can evaluate it at the Facility. Second best is to send a slide, along with a description or image of the component(s) to be identified. Please address your package to Mark Shapley, CSD Facility, 116 Church Street SE, Tate Hall Room 175, Minneapolis MN 55455, USA, 612-626-7889. I can’t guarantee the safe return of slides or material, due to the vagaries of the post and TMI’s limited shipping budget.
We know that our breakdown of “organic identification types” into Arthropod, Fish Other invertebrate/protist, and Plant, is polyphyletic, somewhat arbitrary, and likely to make biologists cringe. However, it is a useful organizational scheme for the purposes of identifying components in smear slides, and our main responsibility is to the smear slide describer. Contributions, advice and suggestions from biological subject matter experts are welcome any time.
The availability of inexpensive “desktop” SEMs is making electron microscopy a more common part of core description and analysis. Recent additions to the TMI catalog include SEM images under the same component organization and tagging system as the light-microscope images. We anticipate adding many more SEM images with future updates.
There’s a lot of overlap in the inorganic components marine and lacustrine sediments. Detrital materials, including siliciclastics, detrital carbonates, many diagenetic minerals, and volcanic materials, are found commonly in both lakes and oceans. For the most part, then, TMI does not specify a marine, lacustrine, or estuarine source for component images.
The primary differences lie in salts and in biological components. For example, carbonate in the oceans is mainly in the calcite and aragonite tests of organisms, while in lakes, inorganically precipitated carbonates (including a variety of carbonate minerals in addition to calcite and aragonite) dominate. The highly variable chemistries and brine evolution pathways of lakes can lead to precipitation of a number of salts not normally found in ocean settings. In terms of biological components, diatoms, sponges, and ostracodes occur in both lakes and oceans, but of different taxa. Some organisms such as coccoliths, foraminifera, pteropods, radiolarians, and silicoflagellates are usually marine (although they can occasionally be seen as detrital components in lakes with fossiliferous bedrock, and may grow in lakes with marine water input). Where necessary, the component description includes notation of the restricted origin of a given component.
We use “lithofacies” to denote a description of a whole sediment as seen in a smear slide, within the sediment classification scheme of Schnurrenberger et al (2003) for lacustrine sediments. Lithofacies can tell you a lot about the depositional environment; in the coming months we plan to add coupled lithofacies images with core face images of sedimentary structures in order to show sedimentary facies.
116 Church Street NE, Minneapolis, MN 55455
P: 612-626-7889