Minerals are naturally occurring chemicals with a definite crystal form.

Rocks are composed of one or more mineral.

Minerals have distinctive physical and optical features that can be used to identify them. Some physical features to note when looking at a hand specimen of a mineral are:

Shape - nice crystal/ rounded/in between
Colour -
Transparency - opaque, translucent, transparent
Hardness - is it hard or soft
Texture - rough, smooth, metallic, glassy.
When we look at rocks some features to note are:
Colour
Density - is it heavier or lighter than it looks?
Texture - is it fine or coarse grained?
Are the grains angular or rounded?
Are the grains interlocking, or are they cemented together?
Is there any layering?
Are the minerals separated into layers or patches?

There are lots of scientific jargon words we can use to describe rocks and minerals, but if you don't know what they are just use your own words. Your first impressions of the specimen are important - what makes it distinctive? But, do not be too concerned about getting the "right" name for the rock, mineral or fossil - just observe and describe. Once you decide what to call it - there is a great temptation to start describing the feature you think it should have, rather than make your own observations.

There are three major sorts of rock - Igneous, Sedimentary and Metamorphic.

Igneous rocks form from molten magma or lava and are made up of interlocking crystals of minerals. If it formed within the surface of the earth, cooling slowly the crystals will be large, but if it cooled rapidly it will be very fine-grained or even glassy. "Acidic" igneous rocks (such as Granite) tend to be pale coloured and tend to form in continental conditions. 'Basic' rocks (such as basalt and Gabbro) tend to be darker in colour, or greenish and form in oceanic conditions.

Sedimentary rocks, are made up of the weathering and erosional products of other rocks. They tend to have rounded grains which are held together by a cement. They are often layered and may contain fossils or trace fossils. Examples are - Sandstone, Limestone, Clay, Shale, and Chalk.

Metamorphic rocks have been altered by heat and pressure. New minerals have started to appear. There may be some re-orientation of the texture to give a new layered structure. Examples are Slate, Gniess, Schist, and Marble.

Some diagnostic features of some rock forming minerals:

Quartz - Clear or greyish, glassy, hard.
Feldspars - hardish, white or pink, translucent.
Hornblende - dark, hard, Amphibole Group
Augite - dark or dark green, hard, Pyroxene Group
Muscovite - clear or white, soft, flaky, Mica Group
Biotite - brown, soft, flaky, Mica Group
Calcite - clear or white, softish, good rhombic cleavage, reacts with acid.
Clay minerals - very small crystals, pale coloured, earthy, plastic when wet.

Some features of common rock types:

Igneous -

General - dark ones are 'Basic', greenish ones are 'Ultrabasic', pales ones are 'Acidic'.- coarse grained ones are 'Intrusive', fine grained or glassy ones are 'Volcanic' or 'Extrusive'. They can be classified by their mineral content.

Sedimentary -

Sandstone - grains of quartz and other minerals cemented together, colour - red, buff, white, green.
Conglomerate - rounded pebbles of rock cemented together
Breccia - angular pebbles of rock cemented together
Clay - soft, earthy, dark or brown or pale, plastic when wet.
Shale - clay in thin layers, looks like pages of book, dark, soft.
Limestone - soft, reacts with acid, usually contains fossil shells.
Oolite - buff coloured (or black) limestone, looks like it is mad of fish eggs.
Chalk - soft, white, fine grained limestone
Till/Tillite/Boulder Clay - dumped by glacier, poorly sorted mixture of clay, pebbles and boulders, as seen at Hornsea,

Metamorphic -
Slate - dark, splits into sheets, as seen on (or blowing off) roofs, harder than shale.
Schist - darkish, tends to have distinctive layers of mica
Gneiss - dark and light layers
Marble - usually light coloured, softies, reacts with acid; recrystallised limestone.
Quartzite/Metaquartzite - hard, usually light coloured; recrystallised sandstone.

The Rock Cycle

Describing rocks