We report on the relationship between the backscattering coefficient at 665 nm and the cross sectional area of particles in suspension in the Irish Sea, Celtic Sea and English Channel. A plot of the backscattering coefficient against particle area shows two distinct trends: one for particles with high mineral content and another for particles with low mineral content. Backscattering per unit particle area (effective backscattering efficiency, Qbb) shows a continuous non-linear dependence on the ratio of mineral to total suspended solids (MSS/TSS) over the range 0.35 <MSS/TSS <0.91. The relationship can be represented by an exponential function: Qbb = 0.000087 exp(6.9 MSS/TSS), which explains 62% of the observed variance in backscattering efficiency. Changes in particle size have no significant influence on Qbb. As the MSS/TSS ratio increases, the backscattering ratio (bb/b) also increases. The implication for the quantitative remote sensing of marine suspended sediments is that the mass specific backscattering coefficient, bb* depends on the particle area per unit mass multiplied by a function which depends on the mineral content of the particles.