Stannite or cassiterite
Stannite is a steel-grey tin sulphide, hardness 4, with a blackish streak. Cassiterite is tin oxide, hardness 6 to 7, density near 7, with a pale streak.
Stannite or cassiterite? Streak and heft decide. Stannite, Cu2FeSnS4, is a steel-grey to iron-black metallic sulphide, hardness 4, density 4.3 to 4.5, with a blackish streak. Cassiterite, SnO2, is hardness 6 to 7, density 6.98 to 7.01, with a white to pale brown streak. A 20 g piece reads 15.35 to 15.56 g in water against 17.13 to 17.15 g.
In short
- The streak-and-heft rule: a dark streak on a lighter piece is stannite; a pale streak on a heavy one is cassiterite. The Handbook of Mineralogy gives stannite a blackish streak and density 4.3 to 4.5, and cassiterite a white, pale brown or pale gray streak and density 6.98 to 7.01, even when the cassiterite itself is black.
- The scale gap is 1.57 g on a 20.00 g piece. Calculated as mass times one minus one over density, stannite reads 15.35 to 15.56 g in water and cassiterite 17.13 to 17.15 g.
- Cassiterite is the tin ore; stannite carries far less tin. Worked on standard atomic weights, cassiterite is 78.77% tin and stannite 27.61%, which the stannite sheet prints too: 2.85 times as much tin per gram. The cassiterite sheet calls it the principal ore of tin; the stannite sheet says stannite may constitute an ore mineral at a number of Cornish mines.
- A hardness spot confirms it. Stannite is 4, softer than a steel point at about 5.5; cassiterite at 6 to 7 is not marked by steel. Lustre helps: metallic on stannite, adamantine to adamantine metallic and splendent on cassiterite, greasy on its fractures.
- The harder question is which stannite. Five rows of the IMA list share the formula shape Cu2XSnS4, and stannite and ferrokësterite print the identical formula. Kësterite, greenish black with a black streak, reads 15.59 to 15.64 g in water. These need a laboratory.
| Criterion | Stannite | Cassiterite | Kësterite (Handbook: kesterite) | Does it choose? |
|---|---|---|---|---|
| Formula, Handbook; IMA list | Cu2FeSnS4; Cu2FeSnS4 (G, 1832) | SnO2; SnO2 (G, 1832) | Cu2(Zn,Fe)SnS4; Cu2ZnSnS4 (G, 1956) | Only by analysis |
| Class | Sulphide; stannite group | Oxide; rutile group | Sulphide | Not by eye |
| Crystal system; habit | Tetragonal; rarely crystals, to 6 cm, pseudo-octahedral by twinning; massive, granular | Tetragonal; prisms to 10 cm; twins very common on {011}, geniculated | Tetragonal, pseudocubic; massive | Yes, when crystals are present |
| Colour | Steel-gray to iron-black, may tarnish blue | Black, brownish black, reddish brown, red, yellow, gray, white | Greenish black | No: both can be black |
| Streak | Blackish | White, pale brown, pale gray | Black | Yes: the streak-and-heft rule |
| Lustre | Metallic | Adamantine to adamantine metallic, splendent; greasy on fractures | Metallic | Usually |
| Hardness | 4 | 6–7 | 4.5 | Yes: steel marks stannite |
| Cleavage, fracture | Indistinct on {110} and {001}; uneven | {100} imperfect, {110} indistinct; subconchoidal to uneven | Not recorded | No |
| Density, measured | 4.3–4.5 | 6.98–7.01 | 4.54–4.59 | Yes, against cassiterite |
| 20.00 g piece in water | 15.35–15.56 g | 17.13–17.15 g | 15.59–15.64 g | Cassiterite: yes, 1.57 g clear. Kësterite: no, 0.03 g |
| Tin by mass, calculated | 27.61% | 78.77% | 27.02% (Cu2ZnSnS4, not used to choose) | Only by analysis |
| USGS separator, best range | 0.50–0.70 amp (3 samples): paramagnetic | Above 1.70 amp (6 samples): diamagnetic | Not in the table | Only on a laboratory separator |
Stannite or cassiterite: two tin minerals, two chemical classes
Stannite is a copper-iron-tin sulphide; cassiterite is tin oxide. The Handbook of Mineralogy sheet for stannite prints Cu2FeSnS4, tetragonal, in the stannite group, and records it as dimorphous with ferrokesterite. The Handbook of Mineralogy sheet for cassiterite prints SnO2, tetragonal, in the rutile group. The IMA-CNMNC list of minerals gives both formulas exactly as the sheets do, both grandfathered, both from 1832, both with the United Kingdom as country of first description. The stannite sheet marks its type locality as Wheal Rock, near St. Agnes, Cornwall.
Both are tetragonal, so crystal system does not choose; habit sometimes does. Stannite is rarely in crystals, to 6 cm, with a pseudo-octahedral habit due to twinning, and is commonly massive, granular or disseminated. Cassiterite forms prisms to 10 cm and twins very commonly on {011}, the geniculated elbow twins described on cassiterite. Stannite's own page is stannite.
They occur together. The stannite sheet lists cassiterite among its associates, with chalcopyrite, sphalerite, tetrahedrite, arsenopyrite, pyrite and wolframite. Six place names appear in both Distribution fields, counted by reading them side by side: Cornwall, Cínovec (Zinnwald), Zeehan in Tasmania, Llallagua, Oruro and Potosí. A tin-district label does not choose between them; see Cornwall.
How do I tell stannite from cassiterite? The streak-and-heft rule
The streak-and-heft rule: draw the specimen on unglazed porcelain, then weigh it in water; a dark streak and a light piece is stannite, a pale streak and a heavy piece is cassiterite. Stannite's sheet records a blackish streak; cassiterite's records white, pale brown or pale gray, though the crystal itself is commonly black or brownish black. That contrast is the most useful single observation, and the method is on how to use a streak plate.
Worked on a 20.00 g piece. Weight in water equals mass times one minus one over density. Stannite at 4.3 to 4.5 reads 15.35 to 15.56 g; cassiterite at 6.98 to 7.01 reads 17.13 to 17.15 g. The gap, 1.57 g, is wide enough for an ordinary 0.01 g scale; the procedure is on how to measure specific gravity at home. Matrix attached to either shifts the reading, so weigh the cleanest piece you can.
Hardness and lustre agree. Stannite is hardness 4, with Vickers 216 to 265; cassiterite 6 to 7, with Vickers 1239 to 1467. A steel point marks stannite and not cassiterite; the method is on how to test mineral hardness properly. Stannite's lustre is metallic; cassiterite's adamantine to adamantine metallic, splendent, and may be greasy on fractures.
Is stannite a tin ore? Tin per gram, worked
Cassiterite carries 2.85 times as much tin per gram as stannite. On standard atomic weights (Cu 63.546, Fe 55.845, Sn 118.71, S 32.06, O 15.999), SnO2 weighs 150.708 g/mol and is 78.77% tin; Cu2FeSnS4 weighs 429.887 g/mol and is 27.61% tin, the figure the stannite sheet prints in its ideal column. A 20.00 g piece of cassiterite holds 15.75 g of tin; the same piece of stannite, 5.52 g.
What the sheets say about ore. The cassiterite sheet opens its Distribution field with The principal ore of tin; deposits are widespread, and its St. Michael's Mount, Cornwall, analysis is 99.26% SnO2. The stannite sheet says that in Cornwall, at Wheal Rock and a number of other mines, it may constitute an ore mineral. Both are tin minerals; the sheets reserve principal ore for cassiterite. Nothing here concerns value or price.
A separator splits them as well. USGS Open-File Report 99-529, Magnetic Susceptibilities of Minerals (Rosenblum and Brownfield) gives stannite a best range of 0.50 to 0.70 amp over 3 samples, paramagnetic on its definitions, and cassiterite above 1.70 amp over 6, diamagnetic. The report names cassiterite among the dark minerals that are exceptions to extraction below 1.00 amp. That is laboratory separation of 125 to 150 µm grains, not a hand-magnet test; see which minerals are magnetic.
Which stannite? Where home tests stop
A home test can say stannite-type sulphide, not stannite. Every line of the September 2026 IMA list, saved as text with pdftotext -layout, was scanned by script for a formula of the exact shape Cu2XSnS4. Five rows match: černýite (Cd), ferrokësterite (Fe), kësterite (Zn), stannite (Fe) and velikite (Hg). Stannite and ferrokësterite print the identical formula, Cu2FeSnS4, so even a chemical analysis does not separate them; that needs structural work.
Kësterite passes the stannite checks. The Handbook of Mineralogy sheet for kesterite gives hardness 4.5, density 4.54 to 4.59, greenish black, black streak, metallic, and names St. Michael's Mount and the Cligga mine in Cornwall. A 20.00 g piece reads 15.59 to 15.64 g in water, 0.03 g above stannite's heaviest. Treat this as a documented negative: on the sheets' numbers the scale cannot separate them.
Who each answer is wrong for. Cassiterite is the wrong answer for a soft, metallic, steel-grey mass with a black streak. Stannite is the wrong answer for a heavy brown or black crystal with a pale streak, elbow-twinned or not. Neither suits a disseminated grey speck in vein quartz too small to streak; label it tin-district sulphide, untested. The identification pages are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.