Here is some more information about rocks and fossils that we might find doing fieldwork in East Yorkshire. These are not described using scientific terms, but are described here using terms that might be easily understood by someone new to geology.
Igneous rocks -
Granite - this is a pale grey or pink or red rock, with big interlocking crystals.
Basalt - this is a very hard black rock, you can see the crystals if you use a magnifying glass.
Porphyry - the use red or purple or brown or yellowish hard rocks. There are large crystals in a fine grained ground mass. The crystals are often square or oblong or diamond shaped.
Larvikite - when it is wet and shiny. This rock is blue in colour and has large crystals. You can often see it on the shopfronts of Marks and Spencers.
Some metamorphic rocks.
Slate - Slate splits into thin layers, people use it on their roots. It can be grey or purple or green in colour.
Schist - this is a fine to medium grained rock, which has layers of shiny mica crystals.
Gniess - (pronounced nice). This is a medium to large grained rock with alternating layers of dark and light crystals.
Marble-this is a week, crystallised limestone. It has an appearance, a bit like sugar loaf. This rock will fizz, if you put a drop of acid on it.
Some sedimentary rocks.
Sandstone - made of some grains, cemented together. Can be fine, medium or course grained, may be red yellow brown green grey or buff in colour.; may fizz when you test it with acid, if the cement is made of carbonate material.
Conglomerate - very coarse grained rock. The rock fragments in it are rounded.
Breccia - (pronounced brechee-a) a very coarse grained rock. The rock fragments in it are angular.
Siltstone - fine grained.
Mudstone - very fine grained.
Clay - very, very fine ingrained sediment: poorly consolidated. Clay is sticky: when the wet-your boots can get stuck in the wet clay when you are doing fieldwork.
Shale - this is clay, that has been compressed into thin layers. The fossils, that you find in it are often crushed.
Boulder clay - this is just what the name suggests: it is Boulders in clay! This is also known as till.
Limestones - and these are rocks, made of calcium carbonate: they will react with acid. They may well be shelly.
Oolite - this is a limestone made up of little rounded grains, which make the rock look like fish roe.
Chalk - a very fine grained pure white limestone.
Marl - a limey clay; you can find layers of marl in the Chalk of Flamborough Head.
Chert - silica modules or layers, that are found in a limestone.
Flint - this is the name given to Chert, when it is found in Chalk.
Ironstone -a sedimentary rock, that is rich in iron: it is often red or yellow or orange in colour and is heavy. When you pick it up.
Mike Horne, May 2004