10/30/2026
Trent Agate - Oregon’s Arsenic Bearing Rarity
by Bill Hamel
Trent Agate is a rare, single locality vein agate from Lane Co., Oregon, noted for its unusual combination of native arsenic and arsenic sulfide inclusions. Red→orange realgar, yellow orpiment and black→silver-gray native arsenic occur within chalcedony and quartz, making Trent Agate one of the Pacific Northwest’s most distinctive old collection agates.
The included agate was found in the late 1940s and first described in 1950. The locality consisted of a railroad cut and adjacent farm SE of Trent, with organized collecting documented by 1955. Several hundred near vertical agate bearing veins, from a few inches to ~14 inches thick, were worked through pits reaching ~15 ft. Larger veins commonly had broken macro-xln quartz centers bordered by chalcedony.
Trent Agate varies considerably in appearance. The chalcedony/quartz ranges from colorless→gray→blue→black, with red carnelian and rare bluish-gray areas. Realgar commonly occurs as embedded reddish-orange acicular xls, while less common orpiment forms yellow inclusions. Native arsenic occurs as black→silver-gray masses, patches and acicular looking inclusions, commonly surrounded by chalcedony. Minor pyrite may also occur. Some realgar has altered→yellow-orange pararealgar, adding further color variation.
The dark inclusions were historically identified as stibnite because of their metallic appearance and behavior during simple heating tests. Later analysis of tested inclusions found arsenic but no antimony (an essential element in stibnite), identifying the dark material as native arsenic rather than stibnite. The combination of native arsenic, realgar and orpiment suggests that sulfur availability changed during formation: some arsenic combined with sulfur to form sulfides, while some precipitated as native arsenic. This unusual arsenic rich mineral association is Trent Agate's defining feature.
Collectors followed the veins until they narrowed and pinched out. The locality later became overgrown, with no obvious workings remaining, and no significant new supply is expected. Trent Agate is therefore primarily an old collection rarity, generally encountered as older rough, slabs, or polished specimens from long held collections.
Trent Agate contains native arsenic, realgar, orpiment and other arsenic bearing minerals enclosed within chalcedony. Intact or polished specimens are lower risk than material being worked, but should still be handled carefully. Cutting, grinding, drilling, sanding or breaking can release hazardous dust and contaminate saw fluid, equipment, clothing and work surfaces. Use wet methods, effective ventilation, suitable respiratory protection, gloves and careful slurry disposal. Never dry grind, heat, burn, lick or acid treat Trent Agate, and do not reuse contaminated lapidary fluid. Wash hands and equipment after handling, and keep specimens away from food, children and pets. Repeated arsenic exposure can harm the respiratory tract, nervous system, liver and kidneys, while chronic exposure increases cancer risk. Heating Trent Agate can release highly toxic arsenic bearing fumes, while acid treatment may create additional toxic reaction products.
Sources: Howard, D.G. & Tschernich, R.W. (2007) Arsenic in Agate. Micro Probe, 10(6), pp. 2-7 [Trent Agate; SEM-EDS identification of native arsenic]; Staples, L.W. (1950) A realgar & orpiment sagenite. The Mineralogist, 18(10), pp. 492, 494 [Trent Agate; original description]; ATSDR (2007) Toxicological Profile for Arsenic [toxicity, carcinogenicity]; OSHA, 29 CFR 1910.1018 [workplace inorganic arsenic control principles].
Article text & photographs © 2026 Bill Hamel. Authorized for PGMC newsletter & official PGMC social media use only. All other rights reserved.
