Matthiasweilite

matthiasweilite

northstarite

adanite

choloalite

Images

Formula: PbTe4+O3
Tellurite, triclinic paramorph of monoclinic plumbotellurite
Crystal System: Triclinic
Specific gravity: Calculated 7.282 for the empirical formula and 7.313 for the ideal formula
Hardness: 2½
Streak: White
Colour: Light yellow
Solubility: Dissolves slowly in dilute hydrochloric acid at room temperature
Environments

Hydrothermal environments

Matthiasweilite is a new mineral, approved in 2021 and to date (June 2023) reported only from the type locality.

Localities

The type locality is the mine dump of the Delamar mine, Delamar Mining District, Lincoln County, Nevada, USA. The mines in this district principally exploited epithermal fissure veins composed mainly of quartz and containing native gold, native silver, pyrite, chalcopyrite, bornite, chalcocite, tetrahedrite, tennantite, sphalerite and galena, as well as baryte and unidentified tellurides.
A wide variety of secondary minerals has been collected from several mine dumps, including numerous tellurium oxysalts such as adanite, bairdite, burckhardtite, carlfriesite, choloalite, emmonsite, eztlite, fairbankite, frankhawthorneite, jensenite, khinite, kinichilite, kuksite, leisingite, mcalpineite, mojaveite, mullerite, northstarite, paratimroseite, poughite, quetzalcoatlite, rodalquilarite, spiroffite, teineite, tellurite, tlapallite, utahite, xocolatlite, xocomecatlite and possibly zemannite. Other minerals include native tellurium, altaite, and likely hessite.
Matthiasweilite was initially identified on a single micromount-sized specimen in a cavity in quartz in direct association with northstarite. It was subsequently identified on several other small specimens in association with adanite, choloalite and northstarite, and in a polished thin section of partially oxidised primary ore, where it occurs together with northstarite and other oxysalts in close association with altaite, tetrahedrite-(Zn), gold, and other sulphides and selenides. It is interpreted to be a secondary mineral crystallising from solutions rich in lead and tellurium sourced from the oxidation of primary lead and tellurium minerals, such as galena, altaite, hessite, and possibly petzite.
Samples from the Delamar mine reveal a complex mixture of primary sulphides, especially tetrahedrite, with relict tellurides such as altaite and selenides such as naumannite. These have undergone deep weathering to produce a range of oxysalt minerals, varying from simple lead - tellurium - oxygen phases such as matthiasweilite, to complex lead - iron - copper - (selenium silver) - antimony - tellurium - oxygen crusts.
On the holotype specimen, matthiasweilite occurs in tightly intergrown masses of crystals, these being ~0.35 mm across, occupying cavities in quartz (CM 60.805-814).

Back to Minerals