|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
|kerogen (kěr'ə-jən) Pronunciation Key
A fossilized mixture of insoluble organic material that, when heated, breaks down into petroleum and natural gas. Kerogen consists of carbon, hydrogen, oxygen, nitrogen, and sulfur and forms from compacted organic material, including algae, pollen, spores and spore coats, and insects. It is usually found in sedimentary rocks, such as shale.