Obsidian is a naturally occurring volcanic glass, formed when felsic lava cools so rapidly that mineral crystals do not have time to grow. This quick cooling results in a smooth, glassy texture, sought after by collectors and artisans for centuries. Utah’s history of volcanic activity, particularly in its western deserts, has created several accessible sites rich with this unique material. This guide directs you to the most productive collection areas and provides necessary information for a safe and legal rockhounding trip.
Primary Collection Locations in Utah
The most well-known and productive area for finding obsidian in Utah is the Black Rock Desert region of Millard County, situated between the towns of Delta and Fillmore. This expansive area experienced significant volcanism approximately 2.5 million years ago, creating extensive obsidian beds that are now easily accessed by the public. The primary collection sites are concentrated around the Black Spring and Coyote Spring vicinities.
Rockhounds frequently find a range of obsidian types across the hillsides and roadbeds in this area. While deep, clear black obsidian is the most common find, collectors often discover mahogany obsidian, which features a reddish-brown coloration caused by inclusions of hematite or magnetite. Snowflake obsidian, characterized by its black base dotted with white-gray spots of cristobalite, is also plentiful in this volcanic field.
Access to these collection areas is typically via dirt roads off State Highway 257. While a four-wheel-drive vehicle is helpful, especially after rain, many areas are reachable with standard high-clearance vehicles. The obsidian pieces range in size from small pebbles to larger fist-sized chunks, often scattered across the surface, making collection relatively easy. The quantity and variety of volcanic glass make Millard County a premier destination for rockhounding in the state.
Legal and Safety Considerations for Rockhounding
Before collecting any material, confirm the land ownership, as rules vary significantly between federal, state, and private property. Much of the prime obsidian territory in Utah is managed by the Bureau of Land Management (BLM), which permits casual collection for personal use without a permit. The limit on BLM land is 25 pounds per person per day, plus one piece, with a yearly maximum of 250 pounds.
Collecting is strictly prohibited within the boundaries of any National Park or National Monument. State Trust Lands require the purchase of an annual rockhounding permit. All collection must be for personal, non-commercial purposes, and surface disturbance should be negligible, meaning the use of explosives or power equipment is forbidden. Always check for posted signs, and never trespass on private property without permission from the landowner.
Safety while rockhounding in the desert is paramount due to the dry, remote conditions. Always carry a significant supply of water, aiming for at least one gallon per person for a full day trip, and wear sturdy, closed-toe shoes. Because obsidian breaks into incredibly sharp fragments, wearing heavy-duty gloves and eye protection is recommended to prevent cuts and injuries. Be aware of local wildlife, including rattlesnakes, especially when turning over rocks or digging in sheltered areas.
Characteristics for Identifying Obsidian
Obsidian is best identified by its distinct physical properties that differentiate it from other dark volcanic rocks like basalt. The most telling characteristic is its glassy texture and luster, resulting from the rapid cooling that prevented crystalline structure formation. When broken, true obsidian exhibits a conchoidal fracture, meaning it breaks along smooth, curved, shell-like surfaces.
This shell-like breakage allows the edges of the rock to become razor-sharp, a feature historically exploited for tools and weapons. In contrast, basalt, a dark volcanic rock, has a dull, fine-grained texture composed of microscopic mineral crystals. While both can appear dark, basalt does not possess the reflective, glass-like sheen of obsidian. The streak test, where the rock is scraped across an unglazed ceramic surface, can also help; obsidian produces a white streak.