Labradorite is the principal feldspar in tholeiitic basalt from Deep Sea Drilling Project Site 464, on northern Hess Rise. Andesine and oligoclase constitute most primary feldspar in the reportedly trachytic rocks from southern Hess Rise at Site 465. Secondary sanidine(?) has replaced the primary phases at Site 465. The secondary potassium feldspar probably resulted from reaction of trachyte with potassium-bearing hydrothermal fluids or sea water.

Number of cations on the basis of 32 oxygens.

Supplement to: Lee-Wong, Florence (1981): Feldspar compositions of volcanic flow rocks from Hess Rise, Deep Sea Drilling Project Leg 62. In: Thiede, J; Vallier, TL; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 62, 967-970