Non-clastic Rocks

NON-CLASTIC ROCKS

These are based on living things and include organic or biochemical sedimentary rocks. You should be able to recognize limestone, made from calcite and perhaps see biochemical chert, which are silica pieces coming from diatoms or Radiolaria in the ocean. You might see these layered out in some way. The White Cliffs of Dover are made from diatomite, which is made out of layered diatoms. See them in figure 39:

Figure 39

Other major rocks containing chemical cherts are essentially mineralized silica where water has flowed through. Those you might be familiar with are these:

• Flint –this is gray or black due to organic matter.

• Jasper –this is red or yellow due to precipitated iron oxides. There are many kinds of these.

• Agate –this is silica also but with different impurities laid out in concentric rings.

• Petrified wood –this is wood grain in color but is essentially silica.

• Chalcedony –this tends to be white or purple and is also made from silica.