Among the various leisure activities that the state of Oregon boasts of, agate hunting is one of the most thrilling and most enjoyable. While low on monetary value (aside from some exceptional pieces), agates can be used to create stunning jewelry, beads, vases, ornaments, and other artworks. This type of chalcedony is considered to be semiprecious gemstones.
Agate is a concentrically banded form of chalcedony. The term "Agate" is also used for non-banded chalcedony with various types of inclusions such as moss, plum, or flame agate. Unbanded translucent or semitransparent materials with no inclusions that look like agates are chalcedony.
Distinctive bandings, color patterns, and "impurities" make the agate unique and desirable. For example, "angel wing" - agate with a swirled grain is highly-prized. Other rare highly-valued agates: dendritic, sagenitic, moss, and plume.
Composed of silicon dioxide SiO2, agate is a translucent or semitransparent fine-grained microcrystalline or cryptocrystalline quartz. The tough and attractive mineral has excellent working properties, a high hardness of 7 (the Mohs Scale), acid resistance, and retains a polished surface quality.
Generally, agate has distinctive colorful uneven bands or patterns. The color banding can be white, gray, orange, brown, pink, green, purple, black, yellow, and multicolored. Green and blue hues are rare. Embedded minerals, mostly iron oxides are responsible for color tones. Other inclusions are manganese, chromium, celadonite, nickel, copper, and hematite.
Most of the agates formed into cavities of ancient volcanic lava or other extrusive igneous rocks.
The formation of the cavities could be traced back to the formation of the continents. Layers of molten lava containing trapped gases were forced towards the surface of the Earth. As the igneous rocks cooled and hardened, the gases escaped through cracks, leaving hollows behind. The empty cavities were gradually filled with fluids rich in minerals such as quartz (silica), moganite (quartz polymorph), calcite, or zeolites to form amygdules and geodes.
Supersaturated silica created an active crystallization inside the cavity. Tiny fibrous microcrystals attached themselves to the sides of the cavity or seam. The various mineral impurities were collected along bands and formed contrasting rings. A balance between the silica and mineral impurities were a result of the formation of agates with alternating bands.
Angel Wing Agate
A rare material has irregular or sometimes botryoidal (grape-like) surface. When cut, the cross section often looks like plum agates. The material can be found around Graveyard Point, the Oregon-Idaho border.
Carnelian (“flesh” in Latin) Agate
Colored by iron oxides, the agate is a translucent reddish-brown or reddish–orange chalcedony. Found in rivers, on beaches, and in mountains.
Dendritic (“tree-like” in Greek) Agate
The rarest agate has tree-like or fern-like patterns – mineral impurities locked inside. The base is usually colorless, white, gray, and sometimes purple. Found in the Crooked River Area.
Enhydro (“water” in Greek) Agate or Water Agate
Agates with enclosed tiny bubbles of water or air moving around that were trapped inside millions of years ago. Enhydro agates may have other inclusions. Often found on the Oregon Coast.
Agate was formed when the most part of the silica gel drained from the cavity. The remaining small droplets crystallized into solid concentric chalcedony known as "eyes". The other layers of silica were arranged around the eyes.
Bands crystallize into concentric layers, where all bands connect to each other, creating walls similar to the fortifications of a castle.
Holley (Holly) Blue Agate
The beautiful highly-prized material ranges from translucent light blue to opaque purple in color. Holey Blue is found in the hills near the small community of Holley, 4 miles away from Sweet Home. Currently, the collecting area is the private property of the timber company and is closed to collecting.
Rare agate produces a unique iris effect; when the mineral is held towards light, it shows prismatic colors of thin bands.
The rarest translucent agate with embedded green mossy or fern-like inclusions. Due to Moss Agate lacks the banding pattern, it is not a true agate.
The rarest agate contains plume-like mineral inclusions in a variety of colors. The material can be found around Graveyard Point, the Oregon-Idaho border.
The translucent material may have white, pale beige, or blue base colors with sharp or spherical dots of different sizes and colors. Unique Polka Dot agate is produced in Central Oregon at Polka Dot Agate Mine.
Sagenitic (“net” in Greek) Agate
The chalcedony contains fine hair or needle-like mineral inclusions embedded into the agate. This material can be found on the Oregon Coast beaches, in rivers, and in road cuts.
The name refers to a translucent mineral with its surface layer that reminds snakeskin. Unusually shaped nodules are light, beige, or reddish and might contain light concentric bands. The material is found in Rome, Eastern Oregon, and near Prineville, Central Oregon.
A round nodule-like formation filled with different agate, jasper, opal, and/or quartz crystals. Central and Eastern Oregon is the most popular region in the world for thundereggs collecting.
Agate Hunting Locations
The weathering and disintegration of host rocks cause the agate nodule release. Agate can be found lying on the surface of beaches, in rivers and gravel that make them easy to collect.
Oregon is one of the most popular states for agate hunting. There are many public lands you can find gemstones for your collection.
Before accessing the area and collecting any rocks, contact the local agencies to find out the most up-to-date information and regulations.