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.
Conventional CT (also called dynamic incremental scanning), is generated by directing an X-ray beam at several different angles and levels of the abdomen. Contrast dye, given to the patient orally and/or intravenously, helps to make the organs visible by appearing white on the X-ray films.