Obsidian is a naturally occurring volcanic glass that forms when lava from a volcano cools rapidly. This igneous rock is produced from felsic lava that contains high levels of silica, oxygen, aluminum, sodium, and potassium. When the molten lava comes in contact with air or water, it cools nearly instantly, creating a glass with minimal crystal growth. Obsidian is typically jet-black due to the presence of iron oxide, though traces of hematite can give it red or brown colors. The inclusion of tiny bubbles within the glass can also give obsidian a golden, glistening sheen.
The rapid cooling gives obsidian an amorphous, non-crystalline structure that causes it to fracture conchoidally. This means that when it breaks, obsidian creates extremely sharp edges capable of cutting and piercing. In fact, obsidian has been used throughout history to make tools like arrowheads, spear points, and knives. Even today, surgical scalpels made from obsidian produce a smoother, thinner edge that reduces scarring. Beyond its practical uses, obsidian is also prized for its smooth, glassy appearance as a gemstone. When cut and polished, it has a deep black color and vitreous luster.
Obsidian forms near active volcanoes, so most deposits in the United States occur in western states where volcanic activity has occurred. Notable locations include Glass Butte, Oregon; Obsidian Cliff in Yellowstone National Park, Wyoming; and deposits in the San Francisco Volcanic Field of Arizona. Obsidian can also be found at some sites in Colorado, Idaho, Nevada, and California. Knowing an area’s geologic history makes it easier to locate obsidian. Countries like Japan, Mexico, Greece, and Russia also have deposits due to their volcanism.
What is Obsidian?
Obsidian is an igneous rock that forms as an extrusive lava from volcanic eruptions. It has a chemical composition high in silica (silicon dioxide), typically between 70-75% SiO2. Obsidian also contains rhyolite and minerals like magnetite, hematite, hornblende, biotite, and feldspar.
The key characteristic of obsidian is that it cools extraordinarily quickly when lava reaches the surface. With minimal time for crystal growth, the molten rock forms a natural glass with an amorphous structure. The rapid cooling gives obsidian its smooth, uniform texture.
Obsidian’s most notable physical property is its conchoidal fracture pattern. This means that it breaks with curved, shell-like shapes. The fractured edges are extremely sharp, which is why obsidian has been used for tools and blades since prehistoric times.
In appearance, obsidian is typically jet black. But various impurities create other colors like dark brown, brownish-red, and olive green. The presence of iron oxide produces red or black banding. Tiny gas bubbles trapped during cooling can also give some obsidian a golden or silvery iridescent sheen.
Comparison of Obsidian with Other Rocks
|Obsidian||Igneous (volcanic glass)||High in silica, with some feldspar, magnetite, iron oxides||Smooth, glassy||5-6||Conchoidal (shell-like fractures)||Gemstones, lapidary work, tools, medical scalpels|
|Granite||Igneous (intrusive)||Quartz, feldspar, mica, amphibole, other minerals||Coarse-grained, phaneritic||6-7||Irregular||Construction, monuments, countertops|
|Marble||Metamorphic||Recrystallized calcite or dolomite||Non-foliated, granular||3-4||Conchoidal or splintery||Sculpture, architecture, tiles|
|Slate||Metamorphic||Clay minerals, quartz, mica||Foliated, fine-grained||3-4||Slates easily along foliation planes||Roofing, flooring, chalkboards|
|Sandstone||Sedimentary||Quartz, feldspar, rock fragments||Clastic, from cemented sand grains||3-4||Breaks along natural lines||Building stone, paving, architecture|
|Limestone||Sedimentary||Calcite, aragonite, dolomite||Granular, fossiliferous||3||Irregular, fractured||Building stone, cement, sculpture|
- Obsidian is the only volcanic glass, making it unique among these rocks. Its glassy texture and conchoidal fracturing allow very sharp edges.
- Granite is also igneous but very coarse-grained. It has higher hardness than obsidian.
- Marble and slate are metamorphic versions of sedimentary rocks like limestone. Slate has planar cleavage for splitting while marble has recrystallized calcite.
- Sandstone and limestone are softer sedimentary rocks with irregular fracturing. But they have different mineral compositions.
So obsidian stands out due to its volcanic glass origin, smooth texture, hardness, and conchoidal fracturing. These properties lend themselves well to obsidian’s use in lapidary arts.
Hard Yet Brittle
On the Mohs scale of mineral hardness, obsidian falls between 5 and 6, making it relatively hard. But because of its glass-like structure, it is also quite brittle. Obsidian’s hardness allows it to be worked and polished, while its brittleness enables controlled flaking for cutting edges and sharp points.
Obsidian’s amorphous quality also gives it interesting optical properties. Thin pieces can transmit light and have been used as early lenses. Obsidian’s high silica content also makes it highly reflective when polished, something taken advantage of by lapidaries.
Where Obsidian Forms
For obsidian to form, active volcanoes that produce felsic lava rich in silica are required. This makes locations with present or historical volcanic activity the prime spots to find obsidian.
In North America, notable obsidian sources include:
- The western and southwestern United States where the Cascade Range, Sierra Nevada, Rocky Mountains, and other areas contain volcanoes. Notable obsidian locations include Yellowstone National Park, Craters of the Moon in Idaho, and numerous sites in Oregon and California.
- Mexico, where obsidian played an important role in Mesoamerican cultures. Major deposits come from the Trans-Mexican Volcanic Belt.
- Canada and Alaska, which have some minor obsidian deposits.
Other significant global sources:
- The Mediterranean. Greece, Italy, and the island of Lipari all had major obsidian sources that supplied ancient civilizations. Anatolian obsidian was traded as early as 12,000 BCE.
- Japan hosts several famous obsidian lava flows and mountains like Tokachi and Shirataki.
- New Zealand, Papua New Guinea, and Indonesia.
- The Caucasus Mountains. Armenia and Georgia both have archeological obsidian artifacts.
- Ecuador, Chile, and Argentina hold deposits in South America.
A Prehistoric Tool Material
Obsidian played an indispensable role in prehistoric cultures across the globe. Its ability to fracture into extremely sharp edges makes obsidian perfect for cutting tools and weapons. Obsidian blades can be many times sharper than even the best steel razors.
Some of the oldest known obsidian artifacts come from Papua New Guinea and date back over 28,000 years. Obsidian tools and munitions spread with trade, conquest, and migration. Major cultures utilizing obsidian included:
- Indigenous tribes across North and South America
- Mesoamerican civilizations like the Maya and Aztec
- Ancient Greeks, Romans, Egyptians, and Middle Eastern societies
- Pacific island cultures
- Numerous ancient Asian peoples
Obsidian cores and flakes were turned into knife blades, arrowheads, spears, scrapers, engraving tools, and more. Obsidian jewelry also emerged with techniques like carving and drilling holes to make beads.
Obsidian in Lapidary Arts
While obsidian was indispensable for utilitarian tools, its striking appearance also made it ideal for ornamental objects, jewelry, and early artworks. Obsidian was one of the earliest gemstones used by humans.
Cutting and Shaping
Modern lapidaries today carry on this ancient tradition. Obsidian is cut, shaped, and polished using diamond abrasives and specialized equipment. The goal is to maximize obsidian’s natural glassy luster and achieve precise forms.
Cutting styles include:
- Faceting into brilliant cuts like rounds, ovals, and squares
- Cabochons in smooth domed, flat, or free-form shapes
- Carving figures, scenes, abstract shapes, and more
- Inlaying thin slices into pendants, rings, and decorative objects
- Tumbling chunks of obsidian into polished spheres and beads
Lapidaries incorporate obsidian into many types of jewelry:
- Obsidian cabochons are used in rings, pendants, brooches, and other pieces.
- Faceted obsidian makes exceptional jet black gemstones.
- Tumbled stones are threaded into necklaces or bracelets.
- Carved obsidian beads, disks, and pearls are strung into necklaces and malas.
- Thin slices are doubletted with other stones or turned into mosaic-like inlays.
- Unpolished chunks of obsidian are wire wrapped as pendants.
The rainbow sheen varieties like fire obsidian are especially prized. But even plain black obsidian has a sophisticated allure when cut and set into jewelry.
For the home, lapidaries fashion obsidian into:
- Spheres, eggs, pyramids, and carved sculptures as objets d’art.
- Polished tiles for backsplashes, countertops, inlaid floors.
- Decorative bowls, vases, boxes, bookends.
- Fountains, birdbaths, ponds, fire pit linings.
- Aggregate landscaping stones.
When combined with metals like gold or silver, obsidian makes for refined accents and gifts. Obsidian spheres bring a powerful, minimalist touch to any space.
In addition to its aesthetic qualities, obsidian is believed to have healing energies. It is considered a protective and grounding stone.
Some attributes associated with obsidian include:
- Shielding against negativity, emotional trauma, and psychic attacks
- Blocking geopathic stress and environmental pollutants
- Removing blocks and encouraging growth
- Aiding communication and relationships
- Revealing truths and one’s inner self
- Promoting clear thinking and quick decision making
Obsidian is regarded as an empowering stone that can help integrate body, mind, and spirit. It is also thought to connect one with the earth for grounding and centering.
Many incorporate obsidian into meditative and spiritual practices. Tumbled stones are used to make crystal grids and healing layouts. Obsidian spheres bring a symbolic meaning of unity and flowing energy. And obsidian jewelry or palm stones create a portable protective talisman.
The Cutting Edge of Medical Scalpels
While obsidian today is largely used for art, decoration, and crystal healing, it still has some important practical applications. One is for surgical scalpels.
Obsidian can be fractured to produce scalpel blades just microns thick with superfine, feathered cutting edges. In the hands of surgeons, these blades make clean incisions that may heal faster with less scarring compared to steel scalpels.
Obsidian medical blades are also extremely affordable, especially helpful in developing countries. After use, the blades are just disposed of rather than sterilized and reused.
Obsidian: A Distinctive Volcanic Marvel
Obsidian is a true wonder of nature – molten rock frozen into a state of eternal beauty. In the hands of lapidary artists, obsidian is transformed into incredible works of functional art, unique jewelry, and objects of veneration. Its striking form carries both physical and metaphysical significance.
With knowledge of its special properties and origins, we can appreciate obsidian more fully. Obsidian also gives us clues into earth’s past volcanic activity and the ingenuity of ancient cultures across the globe who harnessed this glassy lava rock to their benefit. For all these reasons, obsidian remains a much-loved treasure of the mineral world.