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650șC 30 mins |
Description
Obsidian is a natural glass formed when volcanic lava cools very rapidly, so rapidly in
fact that there is no time for the formation of crystals. Its name comes from the Greek
word opsianos which means 'vision', and refers to the use of polished Obsidian
for mirrors. The commonest colour is black, but it also occurs in brown, grey, and very
rarely red, blue or green. Obsidian that has embedded bubbles or crystal inclusions is
called Snowflake Obsidian, and red Obsidian, which is rare, is called Mahogany Obsidian.
Rainbow Obsidian contains bands of iridescent colour, ranging though purple, blue, green,
and even occasionally orange. Impurities in the lava may impart a golden or silver
metallic sheen to the stone, or give it a velvety texture instead of the usual high shine.
Splashes of lava that cooled into spheres or teardrops are called 'Apache Tears', and the
stone is sometimes called 'Black Velvet' or 'Black Glass'. This last can be a misleading
term, since although it is technically correct, Obsidian is not the same as the glass
manufactured from silicon dioxide and colourants.
The Science
Obsidian is naturally formed glass, with a chemical composition that varies greatly.
The colour is totally dependent on the composition of the lava, which in turn depends on
the type of rock that melted miles below the surface of the Earth to form the lava. All
sites of past or current volcanic activity are capable of being sources of obsidian,
provided that local conditions are such that the lava can cooled sufficiently rapidly.
An important characteristic of Obsidian is its lack of crystal structure, which allows it to break into pieces with smooth, curved edges (called a conchoidal fracture) which are extremely sharp. These edges are sharper than surgical scalpels or diamond blades.
6.0 to 7.0 on the Moh's Hardness Scale
Care and Cleaning
Soft polishing cloth, plain water rinse or mild solution of soap and
water.
History
Obsidian has been used as far back as the Late Stone Age (Neolithic Period) for
arrowheads, axes and knives. Originally, these tools were made from pieces of shattered
Obsidian, but over time the skill of 'knapping' developed. In knapping (which is also the
method used to produce flint tools), a piece of Obsidian is struck at an appropriate angle
at a point of weakness. The size of the knapped piece depends on how the source stone is
struck. A source stone might be used to produce a single large tool, such as an axehead,
by knapping it all the way round, or several smaller tools such as thin knife blades or
arrowheads.
The Aztecs and the Mayas were using Obsidian 2500 years ago for decoration, religious artefacts, tools, mirrors and jewellery. The Aztecs called it tezcapoctli and used it to make statues and images of Tezcatlipoca, the 'Smoking Mirror', god of the nocturnal sky, ancestral memory, time and the Lord of the North. In one aspect Tezcatlipoca was the patron of warriors with black being the colour symbolic of war, and Obsidian was the material of choice for war clubs and sword blades. Aztec shamans used polished Obsidian mirrors for catoptromancy, a method of divination which interprets patterns and images which appear in mirrors and other shiny objects.
The Maya used obsidian for mirrors and Obsidian tools have been found at ancient Mayan sites in Belize. Since the stone is not found in Belize, archaeologists theorise that the Maya had trade access to Guatemala , Mexico, and Honduras.
Native Americans used Obsidian for knives and arrowheads, and even today some Native Americans believe that 'Apache Tears' are the tears of their ancestors. In the ancient cultures of Mexico Obsidian was called izli, which means 'divine stone' and used it for vases and mirrors, examples of which have been found in ancient Mexican graves.
In the Old World, the term Obsidian was used by Pliny, when describing a rock from Ethiopia. Dr. John Dee, astrologer to Queen Elizabeth I, used Obsidian mirrors for scrying and divination when required to provide advice to the Queen.
Obsidian artefacts are important tracing tools for archaeologists, using a method known as Obsidian Hydration Dating or chemical analysis. Because Obsidian absorbs water at a known rate, the age of an artefact can be determined, and the distribution of pieces of the same age gives valuable information about population patterns and migration. The chemical composition of Obsidian artefacts can be used to trace the routes used for trade, since the location of the source of the artefact can be identified by its chemical composition.
Today, Obsidian is used to make a variety of items ranging from chess pieces to piano keys, as well as being used to manufacture reproductions of Aztec statues, Mayan tools and replicas of Indian artefacts. The ancient use of Obsidian as blades is being revived as well, with Obsidian scalpels being used in some hospitals for surgery.