Defined by Schultz (1969) for montmorillonite samples [current nomenclature for montmorillonite is that it is an Al-rich, dioctahedral smectite with an ideal structural formula of (Al_3.15Mg_0.85)Si₈O₂₀(OH)₄X_0.85.nH₂O with layer charge from primarily octahedral substitutions of Mg] with a large net negative layer charge [-0.80 to -1.20 per unit cell, O₂₀(OH)₄] obtained almost entirely (<0.15 charge from tetrahedral sheet) from cation substitutions in the octahedral sheet, although exceptions were noted. This classification scheme was based on chemical and thermal analysis. The term is obsolete and should not be used. Terms used in this obsolete classification are: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite. See also Part 2 of the Glossary.