<P> As the sediment is transported, the unstable minerals are abraded or dissolve to leave more stable minerals, such as quartz . Mature sediments, which contain stable minerals, generally have a smaller variety of minerals than immature sediments, which can contain both stable and unstable minerals . One measure of this maturity is the ZTR index which is a measure of the common resistant minerals found in ultra-weathered sediments: zircon, tourmaline, and rutile . </P> <P> A sediment sample from the lower (downstream) portions of a stream is likely to be more mature than one found upstream, since the original sediment has been subject to more abrasion as it travels downstream . </P>

An immature clastic rock has well-sorted resistant grains