What is an obsidian rock?

Obsidian is a natural volcanic glass, with silicon dioxide (SiO2) as its main component, usually appearing black. Its formation is closely related to volcanic activity. When lava cools rapidly, there is not enough time to form a crystalline structure, thus forming the glassy obsidian.

Structure of Obsidian:

Amorphous Structure: Obsidian is a type of volcanic glass. During its formation, the lava cools rapidly and does not have enough time to form a crystalline structure, resulting in an amorphous structure, also known as glassy. This unique structure allows obsidian to form very sharp edges when it breaks.

High Silicon Content: The main component of obsidian is silicon dioxide (SiO2), which gives it high hardness and wear resistance. Obsidian typically falls between 5 and 6 on the Mohs hardness scale, harder than steel, allowing it to maintain sharp edges.

Conchoidal Fracture: The fracture pattern of obsidian is called conchoidal fracture, which can produce very sharp edges. When obsidian breaks, the resulting fragments have very sharp edges. This characteristic made obsidian widely used for making tools and weapons in ancient times.

Thermal Treatment: By controlling the heating and cooling of obsidian, a process called annealing can be induced, which helps to relieve internal stress, improve the overall toughness of the material, and maintain the sharpness of the edges.

Edge Geometry: The geometry of the obsidian edge has a significant impact on its sharpness. Thinner, sharper edge angles make obsidian tools or weapons sharper. Skilled craftsmen will carefully shape and refine the edges of obsidian to achieve the best sharpness.

Hydration Layer: When exposed to water or moisture, obsidian forms a thin hydration layer on its surface. This layer, composed of hydrated silicate, may slightly reduce the sharpness of obsidian. However, the hydration layer can also enhance the toughness of obsidian, making it less likely to shatter or break.

Microstructure of Sharpness: The sharpness of obsidian is excellent at the microscopic level. Its edges can be ground to be very thin, even reaching the level of 30 angstroms, which is sharper than many modern surgical knives. This sharpness allows obsidian to cause less trauma when cutting, thus allowing wounds to heal faster and with smaller scars.

These characteristics have made obsidian widely used in history for making various sharp tools and weapons, and even in some modern surgeries, obsidian surgical knives are used due to their unique sharpness and minimally invasive characteristics.

The history of obsidian 

In the Paleolithic era, obsidian was used to make tools and weapons such as blades, arrowheads, and spear tips because of its sharp edges. In prehistoric sites in the Mediterranean and West Asia, tools made of obsidian are very common. For example, in the Franchthi Cave on the Peloponnese Peninsula in Greece, there are discoveries of about 7000 years ago, humans used obsidian to make spear throwers, harpoons, blades, etc.

In Central American cultures, obsidian has a special status. Both the Maya and the Aztecs regarded obsidian as a precious material for making jewelry, tools, and ritual items. The Maya even believed that obsidian mirrors could reveal the future. In ancient Egypt, obsidian was also used to make pharaohs' masks, such as the eyes of Tutankhamun's gold mask, which were made of obsidian.

The symbolic significance of obsidian varies in different cultures. In Indian culture, obsidian is called "Apache Tears," related to a sad legend, the tears of sorrow shed by the lovers of tribal warriors turned into obsidian. In Mexican culture, obsidian is endowed with the meaning of warding off evil and protection, called "Tezca," and the sacrificial knives used by priests were made of obsidian.

There are many types of obsidian, including Apache Tears, Rainbow Obsidian, Fire Obsidian, Snowflake Obsidian, Mahogany Obsidian, and Sheen Obsidian, etc., which have different colors and textures, but all have some common characteristics of obsidian, such as conchoidal fracture, glass luster, and transparent to opaque properties.

In modern times, obsidian is not only used for jewelry making but also, due to its sharpness, sometimes made into surgical knives. The incision of obsidian surgical knives is narrower, with less bleeding, and wounds heal more easily, reducing the possibility of wound infection. However, due to its high cost and high grinding requirements, obsidian surgical knives have not been widely used.

In general, the history and cultural significance of obsidian are very rich. It is not only an important material for ancient civilizations but also a precious raw material for modern jewelry and crafts.

 

Reference

1.  Rafferty, John P. (2012). Rocks (1st ed.). New York, NY: Britannica Educational Pub. in association with Rosen Educational Services. p. 97. ISBN 9781615304929.

2. ^ Raymond, Loren A. (1995). Petrology : the study of igneous, sedimentary, metamorphic rocks. Dubuque, IA: Wm. C. Brown. p. 27. ISBN 0697001903.

3. ^ Brian Cotterell; Johan Kamminga (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved September 9, 2011.