3D models of Grinding Stones - Museum of Stone Tools

Grinding Stones

Stones tools were used extensively in prehistory to process plant foods and other materials. Grinding stones work through friction, reducing a material to powder between two stones.

Grinding stones were used to grind and crush different materials including seeds, bulbs, berries, insects, fibres, and ochre. In hand-grinding, the top stone was small enough to fit in the hand, and usually had a convex surface. The bottom stone was usually concave, and the concavity developed as the stone wore away through use. Grinding stones were usually made from course-grained, abrasive materials such as sandstone or basalt.

Archaeologists refer to grinding stone by different terms depending on the region. In the Americas, the bottom stone is often referred to as a metate, a Spanish term derived from the Nahuatl word metlatl, or ‘grinding stone’. The top stone is referred to as a mano, Spanish for ‘hand’. In Europe and West Asia, archaeologists refer to grinding stones as querns, from Old English cweorn, ‘hand-mill’. The bottom stone in hand-grinding is referred to as a saddle quern, and the top stone a muller, from Middle English mullen, ‘to grind’. The term muller is also used in Australia to refer to the top stone. Many archaeologists prefer to use the generic terms ‘top stone’ and ‘bottom stone’.

Grinding technology from the Neolithic period, from about 10,000 years ago, shifted from hand-grinding to the use of two large and heavy circular stones, called rotary querns, with the top stone—called the runner stone—rotated against the fixed bedstone to grind the grain into flour. The weight of the stones provided the force necessary to grind the grain. Eventually draft animals were used to rotate the stones, and, more recently, stone mills were powered by water. Later millstones were carefully manufactured with grooves on the faces to create a scissoring action to cut through the grains. The grooves themselves are called furrows, with the flat surfaces between them called lands. Smaller cutting grooves are called feathering or cracking, and the repeating geometrical patterns are called harps. These stones were balanced and dressed to exacting standards by specialised stone masons.

As with most stone tool types, human societies often assigned cultural significance to grinding stones. Bottom stones were extensively traded by Aboriginal people in the dry regions of Australia. Many of the sandstone quarries for grinding stones were locations on songlines, and are therefore of great spiritual significance. Bottom stones were shaped into elaborate ceremonial items in ancient Costa Rica, often with animal iconography, and placed in graves. Quern-stones from certain basalt sources in the southern Levant were transported hundreds of kilometres in the Bronze Age, and the stones likely had prestige value.

A mortar is a stone bowl used with a pestle to crush or grind food, spices, or other materials. They appeared at about 22,000 years ago in the Levant, and emerged independently in many regions throughout prehistory. Crushing large or hard food items, such as nuts, can be easier in the confines of a mortar, as exemplified by the acorn processing mortar holes made by First Nations people in bedrock outcrops in California. Modern stone mortars tend to be used to process wet or oily foods such as pesto (the term is derived from pestle) and hummus, or to powder small amounts of material, such as medicine or spices. The basalt cobek (a shallow mortar-like stone dish) and ulekan (a pistol-shaped pestle) are used in Indonesia today to make the chili-based condiment called sambal and the peanut-based sauce called gado-gado. The three-legged basalt molcajete (mortar) and cylindrical tejolote (pestle) are used widely in Mexico to prepare traditional salsas and guacamole; their history links back to the ancient Aztec and Mayan cultures.

Other functions for grinding stones was to pound and process diverse materials such as dried meat and hides, bark, plant fibres and resins, and vegetable and mineral pigments. Ores were crushed in querns and mortars for metallurgical processing, and small personal snuff-querns were used in the Shetlands were held in the lap to grind up tobacco for snorting. Grinding stones were used to shape bone tools by abrasion, and to prepare cutting edges on ground-edge stone axes. In an interesting case of lateral recycling, a woman mortally wounded King Abimelech during an Old Testament battle by climbing a tower and dropping a grinding stone on his head (Judges 9:53).