Sample TH96-001 -- minimal interpretation

NOTE: Some of these images are rather large. Check the sizes before downloading. I could decrease the size, but only at the expense of important details. If you want smaller images anyway, let me know.

Weathered exterior view, reflected light

These images were photographed with a macro lens.

Fig. 1 -- oblique view showing flattened cylindrical shape. The two pink objects sticking out of the top are plasticine to hold the specimen -- oops :-)

Fig. 2 -- top view showing outer surface.

Polished cross section, reflected light

These images were photographed using a reflected light microscope.

Fig. 3 -- cross section (186Kbytes), polished, sawed surface. Opposite end from that in Fig.1. Top of Fig.2. Digitally reconstructed from two images.

Thin sections, transmitted light

The first image (Fig.4) was photographed with a macro lens attached to a camera and a light box to provide illumination. The remainder were photographed with a Leitz polarizing light microscope (i.e. a petrologic microscope).

Fig. 4 -- thin section (125Kbytes) approximately corresponding to the sawed, reflected-light surface in Fig.3 (within a few millimetres). The image is mirrored horizontally because the thin section is being viewed from the opposite side to that in Fig.3.

Fig. 5 -- thin section (322Kbytes) at low magnification, showing finer structure located to the lower left of centre in Fig. 4. Plain polarized light. In plain polarized light, the specimen looks much like it would in normal light, with the exception that pleiochroism (change in colour with orientation) may be observed in some minerals as the specimen is rotated.

Fig. 6 -- thin section (183Kbytes) at moderate magnification, showing finer structure. Plain polarized light.

Fig. 7 -- thin section (334Kbytes) at moderate magnification. Plain polarized light.

Fig. 8 -- thin section (334Kbytes) at moderate magnification. Same location as Fig.7. Crossed nichols. In this illumination mode, one polarizer below the specimen and one above are oriented at 90 degrees to eachother. If aligned with the polarizers, or if optically isotropic, the minerals in the optical path do not allow the passage of light in this mode. In other orientations non-isotropic (anisotropic) minerals cause interference colours, with the colour proportional to the thickness of the thin section, and the difference between the indices of refraction of the crystallographic axes of the mineral in their current orientation with respect to the light. By rotating the specimen, individual mineral grains can be brought into and out of alignment with the polarization.

This mumbo-jumbo means the individual mineral grains can be reliably identified based upon their optical properties (i.e. optical mineralogy). See an optical mineralogy/petrology textbook for details. This image is presented as an example of the techniques that were used, but is not particularly useful without being able to rotate the specimen under the microscope.

Fig. 9 -- thin section (124Kbytes) at high magnification. Similar location to Fig.6, but higher magnification. Plain polarized light.


Comparison of specimen TH96-001 with dinosaur bone microstructure. All illustrations are thin sections in plain polarized light. Each pair of images is at the same magnification.

TH96-001 dinosaur bone low magnification.

TH96-001 dinosaur bone moderate magnification.

Back to the evaluation of Carboniferous bone

Andrew MacRae