Zeolites are a large and complex group of hydrated aluminosilicate minerals that are among the most abundant authigenic silicates in sedimentary deposits. They are so complex that only a superficial summary can be given in this short introduction, and readers are urged to consult the vastly more detailed references provided at the end of the chapter. Both water molecules and cations can be substituted or replaced in most zeolites without disrupting the crystal structure, accounting for their great compositional diversity as well as their widespread use in ion-exchange applications. Their classification and nomenclature has undergone, and continues to undergo, extensive review and revision (e.g., Coombs et al. 1998; McCusker et al., 2001). Although more than 30 different zeolites have been noted from sediments and sedimentary rock, only five are common (analcime, clinoptilolite, heulandite, laumontite and phillipsite) and three others (chabazite, erionite and mordenite) are relatively common (Gottardi and Galli, 1985; Hay and Sheppard, 2001).
Figures & Tables
AAPG Memoir 109 is designed as a practical guide for students and professionals to learn the fundamentals of microscopic examination of sandstones, mudrocks, and associated rocks. With more than 1100 color illustrations, it covers the identification of grains, textures, and structures of clastic terrigenous rocks as well as their diagenetic alteration (compaction, cementation, dissolution, and replacement) and porosity reduction or enhancement. It also provides classification diagrams for formal description of those rocks and their porosity. Although the majority of the outcrop and subsurface examples come from the United States (35 states and Puerto Rico), there are representative photographs from 32 other countries, including many from the offshore areas. The foldout birefringence chart and an included DVD with Powerpoint files of all of the petrographic images provide additional aids for instructors and students.