Some months ago there was received at the National Museum for identification a peculiar rock, evidently a somewhat altered volcanic breccia, so injected with a blue coloring matter as to suggest lapis-lazuli. The manner in which the coloring matter was distributed, a portion of it in the cementing material and a portion actually replacing the original rock fragments, suggested its secondary origin and invited careful tests to ascertain its true nature. Thin sections under the microscope showed the coloring matter to occur as minute scales without crystal form and very irregularly distributed. These had the refractive indices and gave the chemical reactions of lazulite, which is a hydrous phosphate of aluminium, iron and magnesium. It is an interesting occurrence since it closely simulates, as above noted, lapis-lazuli (lazurite), which has, however, a quite different composition.