Whewellite is a mineral known for its needle-like crystal structures. Synonyms for this word include calcium oxalate, oxycalcium, whewelliate, and weddellite. Calcium oxalate describes the chemical composition of the mineral, while oxycalcium is another term for calcium oxide. Whewelliate is the original name given to the mineral in honor of British mineralogist William Whewell, and weddellite is a related mineral with a slightly different crystal structure. Whewellite is found in various geological formations, such as volcanic rocks and limestone deposits. It is also formed in the human body, where it can cause kidney stones if not excreted properly.