These first measurements of specific surface area (SSA) of bulk samples of subsurface marine basalts were undertaken to determine the potential area available for microbial colonization. SSA ranged from 0.3 to 52 m (super 2) /g of basalt with the lowest value coming from pillow basalt and the highest value from breccia. The average for massive and pillow basalts combined was 2.3 m (super 2) /g. The total specific surface area of the extrusive volcanic rocks of the ocean crust is estimated to be 10 (super 24) m (super 2) . This surface area could provide attachment for up to 10 (super 34) cells if cell density is the same as that of experimentally colonized basalt surfaces. Independent measures and calculations of biomass in basalts suggest that cell densities on surfaces are only 10 (super -4) times those in laboratory experiments and, therefore, the surface area of basalt does not limit microbial biomass in the igneous ocean crust.