This diatomite was formed in a fresh water lake and is overlayed by a Tertiary basalt flow. Made up of diatoms of the Melosira species, it is microscopically porous, has a low bulk density and has many uses in agriculture from food additive to soil ameliorant and as a soluble form of pure silica which helps plants resist both fungal and insect attack.
Diatoms are about 10um in size and visible with a good light microscope.
Images are examples of specimens only.
Size and shape may vary.
Specimens are usually no smaller than 75mm in one dimension.