Peperite

[1] The term was originally used to describe rocks from the Limagne region of France,[2] from the similarity in appearance of the granules of dark basalt in the light-coloured limestone to black pepper.

[2] In the 2002 edition of "Igneous Rocks" by Le Maître et al.,[3] the definition is given as "A local term for a tuff or breccia, formed by the intrusion of magma into wet sediments.

[1] When magma comes into contact with wet sediment several processes combine to produce the mixture of sedimentary and igneous clasts which is characteristic of a peperite.

The main mechanism suggested for mingling of the igneous clasts with the sediment is fluidisation, in the sense of particle support and transport by a fluid.

[1] Peperites are found world-wide in sediments with a significant water content at the time of formation associated with igneous rocks covering the compositional range from basalt to rhyolite.