Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and often has a glassy or waxy appearance.
Types of peridotite - Peridotite is a generic name for a number of different rock types. All of them are rich in olivine and mafic minerals. They are usually green in color and have a high specific gravity for a nonmetallic material. Shown above are specimens of lherzolite, harzburgite, dunite, and wehrlite. Image by USGS.