Heat treatment is effective on compositions above the eutectoid composition (hypereutectoid) of 0.8% carbon. Study of structure determines their chemical composition and formula. In music, form refers to the structure of a musical composition or performance. Assaying is analysis of the chemical composition of metals. An example of a product classified according its material composition is a picture frame. Some images contain indications of chemical composition. It involves a change of chemical composition. Petroleum classification according to chemical composition. The landing vehicles carried experiments focusing on cloud aerosol composition and structure. One of the commonly studied chemical composition is Pb. The improvement was based on reducing the surface area of a higher density composition. Bulk lead exposed to moist air forms a protective layer of varying composition. Volcanic rocks are named according to both their chemical composition and texture. Steroids can be classified based on their chemical composition. There is some variance in the exact chemical composition of rhinoceros horns.