Rock cupule

Cupules
Cup marks at the Slagsta petroglyph outside Stockholm, Sweden
Material	Rock
Size	Between 1.5 and 10 cm in diameter
Present location	Every continent except Antarctica

Rock cupules (/ˈkjuːpjuːl/) are artificially made depressions on rock surfaces that resemble the shape of an inverse spherical cap or dome.^[1] They were made by direct percussion with hand-held hammer-stones, on vertical, sloping or horizontal rock surfaces. Cupules are widely believed to be the world's most common rock art motifs, found in huge numbers in every continent except Antarctica. They were produced in many cultures, from the Lower Paleolithic to the 20th century,^[2][3] and they can be found on most lithologies. Similar artifacts from lithic Native American cultures are also known as cupstones.

The word cupule comes from the Late Latin cūpula, meaning "little cask".

Appearances

Cupules are usually between 1.5 and 10 centimetres (0.6 and 4 in) in diameter, although larger specimens are occasionally seen. They occur commonly in groupings that may number several hundred; they may be arranged in geometric formations, such as aligned sets, or they occur in unstructured, random groups.

Some specimens in the southern Kalahari Desert are suggested to be in the order of 410,000 years old,^[4] and those of two sites in central India should be even earlier.^[5] In Middle Paleolithic or Middle Stone Age contexts, cupules occur in Africa and Australia, and are attributable to that era also in Europe.^[6] They seem to become less common in the course of the European Upper Paleolithic, but still occur occasionally.^{[7][8][9][10]} Cupules are extremely common in the Neolithic and the Metal Ages of Europe, Asia and Africa, and in medieval Europe.

Purpose

Little is definitely known about the purpose or significance of cupules. Many meanings or purposes have been suggested in the literature (one review lists 71).

, metates, tacitas, and small solution pans.

Creation

Typically cupules were created by direct percussion, i.e. using hand-held hammer-stones.

Abrasion hardness, indentation hardness and brittleness factor (ratio of the uniaxial compressive strength and the uniaxial tensile strength) combine to determine the “composite hardness index” θ, which governs the production coefficient ρ:

ρ = V θ²

The approximate cupule volume V is determined by:

V = π × d × (R² + r² + R × r) ⁄ 3

in which r = mean radius at rim and d = cupule depth. The mean radius is close to half the sum of two radii measured at right angles to each other. The kinetic energy applied in the production of cupules can be determined experimentally, kinetic energy Ek being the ability of a mass in motion to have a physical effect:

Ek = M v²

in which M = quantity of mass in motion, v = velocity in straight line. It amounts to tens of kilo-Newtons in the case of unweathered quartzite.[14] This cumulative application of focused force has occasionally led to kinetic energy metamorphosis in sedimentary siliceous rocks, a phenomenon first identified in cupules but since recognized in many geological contexts.

References