Sedimentary rocks and minerals
Grains, cements and bedding. These are the rocks that record water, wind, life and time without metamorphosing any of it away.
| Sheet | Name | Formula | Mohs | |
|---|---|---|---|---|
| ST-008 Sedimentary | Sandstone砂岩 Sandstone is a photograph of a current. Every grain in it was moved by water or wind, and three measurements taken in the field — grain size, sorting and roundness — tell you how far it trav Hand specimen | Quartz grains (SiO₂) with a cement of silica, calcite, iron oxide or clay | 6–7 for quartz grains; the rock's resistance is set by the cement | |
| ST-009 Sedimentary | Limestone石灰岩 Limestone is the easiest of the common rocks to identify and the hardest to identify well, because one drop of acid answers the first question and leaves every interesting question untouched Hand specimen | CaCO₃, mostly as calcite, with variable clay, silica and magnesium | 3 (calcite controls everything) | |
| ST-010 Sedimentary | Shale页岩 Shale accounts for more than half of all sedimentary rock in the record and gets almost none of the attention. It is a mudrock — clay minerals, fine silt and often a few percent of organic c Hand specimen | Clay minerals + quartz silt + organic carbon; illite and kaolinite dominate | 2–3 (clay minerals; the rock is soft and scratches with a fingernail in places) | |
| ST-011 Sedimentary | Chert燧石 Chert is a sedimentary rock made of quartz so fine that no individual crystal can be seen at any useful magnification, and that fineness gives it two properties that changed human history: i Hand specimen | SiO₂ as microcrystalline quartz and chalcedony, with minor opal | 7 (quartz hardness throughout) | |
| ST-012 Sedimentary | Dolomite (dolostone)白云岩 Dolostone looks like limestone, breaks like limestone and is used like limestone, but a drop of acid gives it away — or rather, fails to. Its mineral, dolomite, is calcium magnesium carbonat Hand specimen | CaMg(CO₃)₂ — strictly the mineral is dolomite, the rock is dolostone | 3.5–4 (slightly harder than calcite) | |
| ST-013 Sedimentary | Bituminous coal烟煤 Coal is the one common rock that is biological rather than mineral in origin. It is the compacted and chemically altered remains of plants that grew in swamp forests and were buried before t Hand specimen | Variable: carbon 60–80 wt%, plus hydrogen, oxygen, nitrogen, sulphur and mineral ash | 2–2.5; vitrain bands are harder, durain duller and tougher |
