noun: A hard, brittle sedimentary rock consisting of microcrystalline quartz. It is often reddish-brown to green but can also occur in a variety of other colors, especially white, pink, brown, or black. Chert often contains impurities such as calcium, iron-oxide, or the remains of silica-rich organisms. It usually occurs as nodules in limestone and dolomite and has curved fractures.
Origin: 1670–80; origin uncertain
Related forms: chert·y, adjective
Used in a sentence: “Well, the road to your upper pasture is washed out. We gotta go get you a [dump truck-sized] load of chert.”