Summary: A systematic and time-saving procedure for the correlation of optical or other physical properties with chemical composition is outlined, and is applicable even where the composition is complex and involves several variables. The procedure is applied to anthophyllite, for which the following partial regression equations are derived:

γ = 1·7249−0·0130Si+0·0140(Ti+Fe‴+Fe′+Mn)±0·0012,

β = 1·7275−0·0142Si+0·024(Ti+Fe‴)+0·0110(Fe″+Mn)±0·0015,

α = 1·6951−0·0117Si+0·040(Ti+Fe‴)+0·0133(Fe″+Mn)±0·0025, p b(Å.) = 16·44+0·28Si−0·13Mg+0·40(Ca+Na+K)±0·04.

The a and c cell-dimensions appear to be constant, within the experimental error of the available data.