Many igneous rocks recovered during Leg 187 have undergone secondary alteration in a deep marine environment. In these descriptions alteration is defined as the chemical transformation of mineral assemblages due to the percolation of fluids. On the HRVCD forms, rocks are graded according to whether they are fresh (<2% by volume alteration/weathering products) or have slight (2%-10%), moderate (10%-40%), high (40%-80%), pervasive (80%-95%), or complete (95%-100%) alteration. We described the types, forms, and distributions of secondary alteration as well as abundances of vesicles and their mineral fillings and veins. Any changes in alteration styles throughout a section or an igneous unit are also recorded on the HRVCD form.
Alteration of cores was described on a piece-by-piece basis. Descriptions are based mostly on hand-specimen observations; specific clay, zeolite, and carbonate minerals are not generally distinguished, except where crystal morphology allows unequivocal identification. Where additional mineralogical evidence is available from either thin-section descriptions and/or X-ray diffractograms, these identifications were integrated into the HRVCDs. Where appropriate, hand-specimen descriptions were augmented with thin-section observations.