chemical sedimentary rocks form when minerals crystallize out of a solution due to evaporation so here we have three different types of chemical sedimentary rocks in the case of the chemical sedimentary rocks the sediments are actually the ions that are dissolved in solution like we see in this picture here so this is the dead sea so we've got water that is very very salty it's got a lot of sodium and chlorine ions dissolved in it and because it's such a warm area there's a very high rate of evaporation here so as the water evaporates the sodium and chlorine ions can make ionic bonds and form the mineral halite when you have a whole bunch of crystals of halite forming together the name of the sedimentary rock is rock salt okay so the rock salt is really just made of one type of mineral halite that is that is crystallizing as the water evaporates okay the same thing is true for this rock here so the mineral gypsum when it forms very large masses of crystals it's just referred to as rock gypsum limestone is the most common and widespread of these chemical sedimentary rocks limestone is also just made of one type of mineral the mineral calcites calcium carbonate so in this case the the chemical sediments would be calcium ions and carbonate ions dissolved in water and then as the water evaporates off the limestone crystallizes out you have calcite crystallizing in these layers forming the sedimentary rock limestone so these three chemical sedimentary rocks are all inorganic they're forming from completely inorganic processes just evaporation of solution and the forming of ionic bonds between the chemical sediments that were in that solution these rocks are also referred to as evaporites because they are formed from evaporation biochemical sedimentary rocks are also formed from chemicals but these chemicals are derived from fossils okay so the sediments here are fossils all three of these on the top here fossil forest limestone coquina and chalk these are really all types of limestones they're all formed of the mineral calcite but they're formed from different types of fossils so in this example of fossiliferous limestone essentially what we're looking at here is a fossilized coral reef so coral makes the hard parts of its body out of calcium carbonate that it extracts from the ocean water okay so in this case this was buried and fossilized and it recrystallizes all that calcite so it's it's basically formed of calcite but it's chock full of fossils coquina is formed of fragments of shells that have been cemented together usually with calcite cement so coquina is almost kind of like a clastic rock in that but in the case here the the class aren't rock fragments they're actually fragments of shells um so the shells are formed of calcite so the animals that make these shells they can extract the calcium and carbonate from the ocean water to make their shells out of calcite so when those organisms die their shells their hard parts settle down to the bottom of the ocean and over time they can undergo basically a lithification process where all of those shell particles get cemented together with calcite cement chalk is formed from very tiny organisms these single cell algae it's a type of plankton these are called coccolithophores and they live in the ocean and their shells their the little outside shell of the of the algae is made of calcite again so again they're extracting this inorganic substance from the seawater to make their tiny little shells they live in the water column and then when they die they settle down to the bottom and over time you can get these massive very very long periods of geologic time you can get these massive deposits of chalk which are formed from the little shells of these tiny single-celled organisms okay so all three of these are really made of calcite um but they're all formed from fossils this fourth one here is actually made from fossilized plant material so coal coal is a sedimentary rock that forms in swamps okay so a swampy place would be a place where you've got kind of still water you've got a lot of plant material and the plants when they when they drop their leaves or they die that plant material settles down into the swamp and over time it becomes compacted and turns into the sedimentary rock that is called coal so coal is also a biochemical sedimentary rock but in this case it's not formed from animals it's actually formed from plants that lived in swamps