Quartz is so hard that it will easily make a deep scratch in glass. Even if you press hard, a meteorite will at best only make a weak scratch mark. (Use a sharp edge of the rock.) In the photo above, the top scratch was made with a quartz crystal. The next mark was made with a piece of chert, which is another form of quartz. The two scratches at the bottom were made with ordinary chondrites (click on image for enlargement of bottom portion).
tomography. any method that produces images of single tissue planes. In conventional radiology, tomographic images (body-section radiographs) are produced by motion of the x-ray tube and film or by motion of the patient that blurs the image except in a single plane.
Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient, but can be freely reformatted or manipulated as required. The technique requires delivery of a gamma-emitting radioisotope into the patient, normally through i