Is pentlandite magnetic?
Yes, by USGS: 2 samples pulled at a best 0.01 amp, named ferromagnetic. Only 3 of 377 rows in its table pull that early. The pentlandite sheet itself is silent.
Yes, on the one measurement there is. USGS Open-File Report 99-529 pulled 2 pentlandite samples at a best 0.01 amp and names pentlandite, (Ni,Fe)9S8, hardness 3.5 to 4, among the ferromagnetic minerals. Only 3 of its 377 table rows have a best range at or below 0.05 amp. The Handbook sheet prints no magnetic property.
In short
- Two sources, one measurement. USGS Open-File Report 99-529 (Rosenblum and Brownfield) ran pentlandite through a Frantz isodynamic separator: total range below 0.01 to 0.30 amp, best 0.01, 2 samples. It names pentlandite with magnetite, maghemite and pyrrhotite as the common ferromagnetic minerals, strongly attracted to a magnet, like a piece of iron. The Handbook of Mineralogy pentlandite sheet prints no magnetic property.
- The three-row line. A script parsing all 377 data rows of USGS Open-File Report 99-529, Table 1 finds 3 whose best range starts at or below 0.05 amp: magnetite (0.01, 6 samples), pentlandite (0.01, 2) and pyrrhotite (0.01 to 0.05, 7). The next best ranges start at 0.10 amp: franklinite, geikielite, hematite and renierite. Pentlandite is on the near side of a gap that no other row crosses.
- Sheet against measurement. Of the three rows, the magnetite sheet prints strongly magnetic and the pyrrhotite sheet magnetic, varying in intensity inversely with iron content. The pentlandite sheet is the only one of the three that is silent. A silent sheet is not a negative result.
- Documented failure: the company it keeps. The sheet says pentlandite is commonly intimately associated with pyrrhotite, and lists magnetite and cubanite, strongly magnetic on its sheet, among its associates. USGS warns that micro-inclusions of magnetite or other ferromagnetic minerals make the lower limit of extraction difficult or impossible to determine. Two samples cannot show that the 0.01 amp belongs to pentlandite alone.
- The decision. Yes, as USGS measured and defines it. Neither source tests a hand magnet. A pull from a bronze-yellow sulfide does not pick pentlandite out from pyrrhotite or cubanite; the streak, pale bronze-brown against pyrrhotite’s dark grayish black, does that, as set out on pentlandite.
| Name (Table 1) | Total range (amp) | Best range (amp) | Samples | Often-locked flag | Handbook magnetism | Reading |
|---|---|---|---|---|---|---|
| Magnetite | Below 0.01 to 0.05 | 0.01 | 6 | * | Strongly magnetic | Ferromagnetic (USGS names it) |
| Pentlandite | Below 0.01 to 0.30 | 0.01 | 2 | None | None printed | Ferromagnetic (USGS names it) |
| Pyrrhotite | Below 0.01 to 0.70 | 0.01 to 0.05 | 7 | None | Magnetic, varying in intensity inversely with iron content | Ferromagnetic (USGS names it) |
| Franklinite | 0.01 to 0.40 | 0.10 to 0.20 | 7 | None | No sheet used | Next row out |
| Geikielite | 0.025 to 0.60 | 0.10 to 0.30 | 1 | None | None printed | Next row out |
| Hematite | 0.025 to 0.50 | 0.10 to 0.30 | 11 | * | None printed | Next row out |
| Renierite | 0.05 to 0.60 | 0.10 to 0.30 | 1 | None | Magnetic | Next row out |
| Chalcopyrite (associate) | 0.30 to 1.70 | 0.70 to 1.30, depends on chemistry | 8 | None | None printed | Paramagnetic range |
| Cubanite (associate) | No row | No row | 0 | — | Strongly magnetic | Not measured by USGS |
| Troilite (associate) | No row | No row | 0 | — | None printed | Not measured by USGS |
Is pentlandite magnetic? What USGS measured
USGS pulled pentlandite at a best 0.01 amp and names it ferromagnetic. USGS Open-File Report 99-529 (Rosenblum and Brownfield) ran 1084 samples of 378 mineral species through Frantz isodynamic separators, on grains of 125 to 150 micrometres at a 15° side tilt. Pentlandite’s row: total range below 0.01 to 0.30 amp, best range 0.01, 2 samples, with no often-locked flag and no depends-on-chemistry note. The report defines ferromagnetic as minerals strongly attracted to a magnet, like a piece of iron, and names magnetite, maghemite, pyrrhotite and pentlandite as the common ones.
The other definitions. Paramagnetic minerals are less magnetic and separable at field currents up to 1.70 amps, the highest current a Frantz separator reaches; diamagnetic minerals are nonmagnetic at 1.70 amps. The report is concerned with practical separation, not with susceptibility in physical units. That is the sense in which this page answers yes.
Consistent with the nickel rows. The same table’s nickel minerals, with pentlandite among the 3 that are pulled, are set out on is millerite magnetic and not repeated here. The species facts, the iron–nickel split and the pyrrhotite streak test are on pentlandite.
How strong is that? The three-row line
Only 3 of the table’s 377 rows have a best range starting at or below 0.05 amp, and pentlandite is one of them. Method: a script parsed every data line of Table 1, read the lower bound of each best-range cell (below 0.01 counted as 0.01) and kept rows at or below 0.05. Result: magnetite, best 0.01, 6 samples, flagged often locked with other species; pentlandite, best 0.01, 2 samples; pyrrhotite, best 0.01 to 0.05, 7 samples. Widening the cut to 0.10 adds franklinite, best 0.10 to 0.20; geikielite, hematite and renierite, each best 0.10 to 0.30. Nothing falls between 0.05 and 0.10.
The total ranges. Four rows have a total range starting below 0.01 amp: the same three and vonsenite, whose best range is 0.20 to 0.30. Pentlandite’s total range closes at 0.30 amp, pyrrhotite’s at 0.70, magnetite’s at 0.05. USGS reports these ranges; it does not rank the three against one another, and neither does this page.
Not the same as the other pages. The gap between hematite and magnetite is the subject of is hematite magnetic, the chromite samples that pull and do not on is chromite magnetic, ilmenite’s titanium rows on is ilmenite magnetic and the ferberite–hübnerite rows on is wolframite magnetic. None of their assets is repeated here.
Why does the pentlandite sheet say nothing?
The sheet is silent where the measurement is not. The Handbook of Mineralogy pentlandite sheet gives (Fe,Ni)9S8, cubic, massive and granular, parting on {111}, hardness 3.5 to 4, density 4.6 to 5.0, pale bronze-yellow, streak pale bronze-brown, and no magnetic property. Of the three-row line, the magnetite sheet prints strongly magnetic and the pyrrhotite sheet magnetic, varying in intensity inversely with iron content. The pentlandite sheet is the one that is silent. This page does not explain the silence; it records it.
Documented failure: the company it keeps. The pentlandite sheet says it is commonly intimately associated with pyrrhotite, and its association line names pyrrhotite, troilite, chalcopyrite, cubanite, mackinawite and magnetite. The cubanite sheet says strongly magnetic and places cubanite in pyrrhotite–pentlandite ores. USGS warns that when micro-inclusions of magnetite or other ferromagnetic minerals are present it is difficult or impossible to determine the actual lower limit of extraction. Table 1 gives pentlandite no often-locked flag, but 2 samples cannot show that the 0.01 amp belongs to pentlandite alone.
What is not measured. Cubanite, troilite and mackinawite have no Table 1 row. The troilite and mackinawite sheets print no magnetic property. The site-wide summary of which sheets record magnetism is on which minerals are magnetic.
How to read a magnet on a pentlandite specimen
A pull is consistent with pentlandite, and equally with pyrrhotite, cubanite or magnetite in the same piece. Neither source tests a hand magnet, so this is a reading of the records, not a test result. Pentlandite is pale bronze-yellow with a pale bronze-brown streak, hardness 3.5 to 4; pyrrhotite bronze-yellow to pinchbeck-brown with a dark grayish black streak, 3.5 to 4.5; cubanite brass-yellow to bronze-yellow, 3.5; magnetite black. The streak is the separation that works; the method is on how to use a streak plate.
Weight will not help. A 20.00 g piece reads 15.65 to 16.00 g in water as pentlandite, 15.63 to 15.70 g as pyrrhotite and 15.04 to 15.22 g as cubanite, and the pentlandite sheet calls pentlandite commonly intimately associated with pyrrhotite. Whether pyrrhotite itself always pulls is a separate question, with its own sources, on is pyrrhotite magnetic; the arsenic minerals of the same ores are on is arsenopyrite magnetic.
On the label. Write pentlandite when the colour, the streak and the context agree, whatever the magnet does. The magnetism questions are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.