Multiple choice Which of the following types of rocks is an organically formed sedimentary rock? Gypsum Mudstone Limestone None of these Reveal answer Fill a bubble to check yourself C Correct answer Explanation Limestone is an organically formed sedimentary rock created from the accumulation of marine organism shells and skeletal fragments. Gypsum (A) is chemically precipitated, Mudstone (B) is clastic - both are not organically formed.