"Kimberlite intrusives are generally exposed over relatively small surface areas. They occur in the form of pipes, dikes, and sills that they may crop out over an area of a few hectares at the most. Other diamondiferous host rocks exhibit similar characteristics. For example , lamproite, another host rock, may occur in the form of dikes, sills, and small volcanoes . But lapmproite are much rarer than kimberlite."