Formula: ([Hg1+]2)3OCl3(OH)
Hydroxyhalide, forms a series with kadyrelite
Specific gravity: 8.33 to 8.45
Hardness: 2½
Streak: Yellow to greenish yellow
Colour: Yellow, orange-yellow, brown, turns dark brownish, then black, on exposure to light, yellow-brown to brown in transmitted light
Solubility: Decomposed by acids with separation of calomel

Sedimentary environments
Hydrothermal environments

Eglestonite is an oxidation product of other mercury minerals such as native mercury and cinnabar (Mindat).


At the Kadyrel' Hg occurrence, Oorash-Khem River Valley, Uyuk Range, Pi-Khem District, Tuva, Russia, eglestonite occurs with lavrentievite, calomel, mercury and kadyrelite (HOM).

At the Funderburk prospect, Pike county, Arkansas, USA, eglestonite occurs in fractures in sandstone with artsmithite and other mercury minerals (Minrec 35.4.344).

At the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county, California, USA, eglestonite is most often associated with edgarbaileyite, native mercury, cinnabar and wattersite coating quartz cavities (Minrec 36.4.346-347).

At the Challenge deposit, Redwood City, San Mateo county, California, USA, eglestonite is associated with cinnabar, mercury and calomel (HOM).

At the type locality, the Terlingua Mining District, Texas, USA, eglestonite is associated with calomel, mercury, terlinguaite, montroydite and calcite (HOM).

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