Clay
Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired and/or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic materials which do not impart plasticity may also be a part of clay deposits.
Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. These solvents (usually acidic) migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits. from wikipedia
In: industrial rocks and minerals · Tagged with: Ceramic materials, clay, Natural materials, Sculpture materials, Sedimentology, Sediments, Silicate minerals, Types of soil
Boulder
In geology, a boulder is a rock with grain size of usually no less than 256 mm (10 inches) diameter. While a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones. The word boulder comes from Middle English “bulder” which was probably of Scandinavian origin such as dialectal Swedish “bullersten” meaning “noisy stone” (Imagine a large stone in a stream, causing water to roar around it) from “bullra” (to roar, cf. Dutch “bulderen”, with the same meaning) and “sten” (stone).
In places covered by ice sheets during Ice Ages, such as Scandinavia, northern North America, and Russia, ice has moved and formed granite boulders, also named glacial erratics. One of the largest is used as the pedestal of the Bronze Horseman in Saint Petersburg, Russia.
Some noted rock formations involve giant boulders exposed by erosion, such as the Devil’s Marbles in Australia’s Northern Territory, the Wairere Boulders in New Zealand, where an entire valley contains only boulders, and The Baths on the island of Virgin Gorda in the British Virgin Islands.
The climbing of large boulders often requires months or even years of practice, and has given rise, since the late 19th century, to the sport of bouldering.
In: industrial rocks and minerals · Tagged with: boulder, large stone