Galena

How to identify galena: the three-check rule

Check one, the streak. Draw the specimen across unglazed porcelain. Galena leaves a lead-grey line. Across the 176 Handbook sheets in this site's reference set (method: each sheet converted with pdftotext -layout, the Streak field searched case-insensitively for lead-gray), four record a lead-grey streak: galena, stibnite, chalcocite and covellite. A black streak points away from galena, towards acanthite or tetrahedrite; a bluish grey one towards molybdenite. The technique is on how to use a streak plate.

Check two, the cleavage. Galena's perfect cleavage is on {001}, which in a cubic mineral is three planes at right angles, so a broken galena is a set of stepped cubes with bright flat faces. Stibnite and covellite each cleave on one plane, and chalcocite's cleavage is indistinct. See cleavage or fracture: how to tell.

Check three, the weight. Galena's measured density is 7.58. Stibnite is 4.63, chalcocite 5.5 to 5.8 and covellite 4.6 to 4.76, so galena is at least 30% denser than any of the other three lead-grey-streak species. The heft is obvious in the hand, and a proper measurement is on how to measure specific gravity at home. A grey metallic specimen that passes all three checks is galena; the table above lists what fails which check.

How heavy is galena? Fifth of 173 sheets

Method. The measured-density field, D(meas.), was parsed by script from all 176 sheets in the reference set, taking the upper end of any range. 173 print a number; berthierine, clinoatacamite and freibergite print n.d., and none of the three has a calculated density above 5.41. Galena, at 7.58, is fifth. Above it are gold at 19.3, silver at 10.1 to 11.1, uraninite at 10.63 to 10.95 and copper at 8.95: three native metals and an oxide of uranium. Galena is the densest sulphide in the set and the densest of its 19 lead species; wulfenite reaches 7.5 at the top of its range, mendipite and mimetite 7.24.

A worked comparison you can use with a ruler. Mass is volume times density. A cube 2 cm on an edge is 8 cm³, so it weighs 8 × 7.58 = 60.6 g in galena, 46.4 g at chalcocite's upper figure of 5.8, 39.8 g in tetrahedrite at 4.97 and 37.0 g in stibnite at 4.63. Galena is 63.7% heavier than stibnite for the same size. The one grey metallic mineral in the table that comes close is acanthite, silver sulphide, at 7.20 to 7.22: black streak, sectile, and no cubic cleavage.

The weight has a practical side for storage: a heavy, soft, perfectly cleaving specimen puts force on its own corners every time it moves. Is galena toxic explains why the fragments that result matter more than the crystal.

Is galena a mineral, and what is it made of?

Yes: galena is a valid mineral species. The September 2026 IMA-CNMNC Master List lists it as PbS, grandfathered, with a question mark for the year and unknown for the country of first description. The Handbook says galena is a Latin word given to lead ore or to the dross from melted lead.

By mass it is 86.60% lead and 13.40% sulphur. On standard atomic weights, lead 207.2 and sulphur 32.06, PbS has a formula mass of 239.26, and 207.2 / 239.26 = 86.60%. The Handbook's ideal column prints exactly Pb 86.60 and S 13.40. Its two real analyses sit close: 86.50% lead from Katanga Province in the Congo, and 85.9% from the Barrow mine, Newlands, Cumbria, by electron microprobe, which also found 0.7% antimony and 0.2% bismuth.

Galena forms a series with clausthalite, PbSe, in which selenium replaces sulphur; the IMA list records clausthalite as grandfathered, 1832, Germany. Clausthalite is not in this site's reference set, so its properties are not given here.

Galena crystals: cubes, octahedra and twins

The Handbook describes galena as most commonly cubic, with crystals to a metre on an edge known; more rarely cubo-octahedral or octahedral; sometimes tabular on {001}, and also as reticulated masses and skeletal crystals. Massive galena is cleavable, coarse to very fine granular, and occasionally fibrous or plumose.

Twinning is recorded on two laws: on {111}, as contact and penetration twins, and on {114}, lamellar. The general case is on mineral twinning explained.

Hardness 2.5 to 2.75 puts galena below calcite at 3, so calcite, sphalerite, pyrite and quartz among its associates will all scratch it. Galena is brittle with a subconchoidal fracture where it does not cleave. The sheet's reflectance figures for polished galena run from 51.9% at 400 nm down to 42.6% at 700 nm. The test is on how to test mineral hardness properly.

Where galena is found, including the British localities

The sheet's occurrence line is broad: in many different types of environments, in hydrothermal veins formed over a wide range of temperatures, in contact metamorphic deposits, rarely in pegmatites, and with limestones and dolostones as common host rocks. Associates are sphalerite, marcasite, pyrite, chalcopyrite, tetrahedrite, silver minerals, siderite, calcite, dolomite, baryte and quartz.

The Handbook says only a few deposits of note can be mentioned, and names: the Coeur d’Alene district in Idaho; Leadville and Breckenridge in Colorado; the Tri-State district at Joplin, Missouri, Galena in Kansas and Picher in Oklahoma; brilliant crystals from the Sweetwater mine and the Viburnum Trend in Missouri; Příbram in the Czech Republic; Freiberg in Saxony, Bad Ems, and St Andreasberg, Neudorf and Clausthal in the Harz; Pontgibaud in France; Alston Moor, Cumbria, and Wanlockhead, Dumfries; the Mogul mine at Silvermines, Co. Tipperary; and Naica and Santa Eulalia in Chihuahua.

That list is explicitly a selection. This site's locality notes on Derbyshire and Weardale describe both as lead orefields in which galena was the economic mineral; those are our own locality notes, not Handbook entries. The rest of the sulphides are indexed at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.

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