1 PET scans may also be done to see whether surgery can be done to remove a tumor. 2  Help diagnose Alzheimer's disease when the symptoms are not clear or when a person has dementia symptoms at a young age (usually younger than 65). 3  This is called amyloid imaging.
1 Allochemical rocks are those that contain grains brought in from elsewhere (i.e. similar to detrital grains in clastic rocks). 2  Orthochemical rocks are those in which the carbonate crystallized in place. 3  Allochemical rocks have grains that may consist of fossiliferous material, ooids, peloids, or intraclasts.any limestones (carbonate rocks in general) show characteristics similar to those of clastic sediments, like sandstones. Sandstones are composed of sand grains, a mud or clay matrix, and a crystalline cement produced during diagenesis.
Clastic sedimentary rocks contain clasts. These are fragments or pieces of rock or minerals. The composition of clastic sedimentary rocks is divided into three types-clay/silt, sand and gravel. Clay and silt are less than 1/16 mm.