Heavy Mineral Analysis

A method of analysis carried out on artifacts such as potsherds to identify the materials used; the shard is crushed and put into a viscous fluid in which the heavier minerals sink to the bottom. It is used to determine the geological source of the sand inclusions in the clay of the pot, and therefore the probable area of manufacture. The method involves the crushing of 10-30 g. of pottery and the floating of the resulting powder on a heavy liquid such as bromoform with a specific gravity of 2.85. Heavy minerals like zircon, garnet, epidote, and tourmaline sink, while quartz sand and clay float: it is the heavy minerals (separated, identified, and counted under a low-power microscope) which characterize the parent formation, and which enable the source of the sand to be identified.

Technique of petrological analysis. If rock, ceramics or other mineral-bearing materials are crushed and then mixed with suitably high-viscosity fluid, the minerals in them will separate. Those that sink to the bottom are called the ‘heavy minerals’, and very conveniently these also happen to be the minerals which are most variable in their occurrence. The particular suite of heavy minerals may thus frequently be used to classify a rock or piece of pot fabric, and compare it with others. In archaeology, the method has mainly been used to classify pottery and identify the source of its raw materials.