| The Monterey is unusual in that it has Silica as a major component, which came from the skeletal remains of tiny creatures called Diatoms. These skeletons have the shape of hollow pillows. When hundreds of thousands of them are together in a mass, you have diatomaceous earth, well known for it's extremely high porosity and low density. Later on, after burial and compression, these diatom masses become altered, forming Opal CT, Porcelanite, and Chert. These forms are much more compact, as the little pillows have been flattened, and they can't get up. The dark Cherts found along the beach can sometimes be mistaken for obsidian but are much harder. There are also Dolomite and Phosphate layers in the Monterey. The Dolomite and Chert layers will fracture when stressed. With the tectonic forces at work along the coast, faults and folds occur which can also result in extensively fractured and shattered zones in these layers. If oil is present when the fracturing occurs or shortly after, the oil can be trapped in the fractures and remain there under pressure. If no oil is present, eventually the fractures will be filled with Calcite. Specimens found with filled fractures are interesting to cut and polish. |
