Septarium is a semi-precious gemstone surface — a Septarian (septarium) semi-precious gemstone slab — cracked-block concretion structure: angular taupe​/​brown-grey claystone segments bordered by bold irregular golden-yellow and black mineral veins (calcite​/​aragonite + iron). Distinctive fossil-concretion mosaic look. slab with a polished finish, often backlit as a feature panel, vanity or bar front. A dramatic decorative stone for interior feature applications.