Which of the following is NOT one of the four types of clastic fragments commonly found in limestone?

Which of the following is NOT one of the four types of clastic fragments commonly found in limestone?

• A. Oolites
• B. Intraclasts
• C. Fossils
• D. Chert

Answer: (D)

Clastic fragments in limestone are grains that come from physical breakup or reworking of carbonate material, known as allochems. Ooids (oolites) are tiny rounded carbonate grains formed by concentric precipitation in shallow, supersaturated waters. Intraclasts are pieces of preexisting carbonate mud or grains that were broken and redeposited. Fossils are fragments of shells or other organic hard parts. Chert, however, is a silica-rich material (quartz) that forms by silica deposition or replacement and is not a clastic fragment derived from carbonate debris. In limestone, chert may occur as nodules, but it isn’t one of the typical clastic fragments formed from carbonate grains, so it isn’t counted among the common clastic components.

Clastic fragments in limestone are grains that come from physical breakup or reworking of carbonate material, known as allochems. Ooids (oolites) are tiny rounded carbonate grains formed by concentric precipitation in shallow, supersaturated waters. Intraclasts are pieces of preexisting carbonate mud or grains that were broken and redeposited. Fossils are fragments of shells or other organic hard parts. Chert, however, is a silica-rich material (quartz) that forms by silica deposition or replacement and is not a clastic fragment derived from carbonate debris. In limestone, chert may occur as nodules, but it isn’t one of the typical clastic fragments formed from carbonate grains, so it isn’t counted among the common clastic components.