translate English to French: Kimberlite formed at great depth and was forced to the surface by volcanic action; it occurs there as pipes, dikes and sills. lamproite – rare type of igneous rock which is one of only two rocks known to host diamonds in primary deposits (the other is kimberlite).
La forme brute ressemble souvent à la forme finale après le polissage, mais les façonnables exigent habituellement plus de travail que les sciables et ont un rendement moindre. feuilletis (ou rondiste) – bande étroite qui entoure le bord du plan séparant la couronne et le pavillon d’un diamant poli.