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.
A Single Photon Emission Computed Tomography (SPECT) scan is a type of nuclear imaging test that shows how blood flows to tissues and organs. A SPECT scan integrates two technologies to view your body: computed tomography (CT) and a radioactive material (tracer). The tracer is what allows doctors to see how blood flows to tissues and organs.