FMF - Friends of Minerals Forum, discussion and message board

[Jean Sendero]

Here is one that I am very curious about. I have recently decided to diversify a little from Mexico and start looking at Peruvian minerals a little more. Why? I have the opportunity to go to Lima every second month for my work. So, when I have some spare time, what better then to start hunting down minerals.

Great sport. However, after visiting the Andres del Castillo Museum and dealers, I was left very perplexed when it came to the Peruvian hubnerite-Ferberite and wolframite. The museum has specimens of each and frankly visually, I could not tell the difference between each.

Dealers here are only offering hubnerite, but are these always hubnerite or can they be the ferberite or wolframite.

Is anyone aware of a way to visually distinguish between all three? or at least between the two extremes of the series?

Thanks

Cheers

Jean

[Matt_Zukowski]

In most instances, you can't visually differentiate hübnerite from ferberite. If you see one that transmits light, it is most likely a low-Fe hübnerite because, I have heard, Fe in the wolframite structure makes the mineral more opaque. I have seen specimens called ferberite that transmitted a reddish light, but I'll bet they were hübnerite. Note that hübnerite can be opaque. I am not aware of any other way to visually distinguish among the wolframites.

Wolframites of various Fe/Mn ratios can appear in the same deposit. So unless I know what mine a specimen comes from, and I know that that mine only produces a limited range along this series, I would label the specimen as wolframite.

[alfredo]

I agree with Matt. If you see any red or red-brown translucency on thin edges under a bright light, it's a hubnerite. If it's black and opaque it could be ferberite or a high-Fe hubnerite. You can try a streak test - Ferberite streak being more blackish brown and hubnerite being more brownish or reddish. But if your sample is near the middle of the series, then you'll need microprobe work to measure the Fe:Mn ratio.

John Attard can get a pretty good idea of a sample's position in the series by its PXRD pattern. As it's only a simple 2-end-member series, without any third substituting elements to confound the unwary, the distortion in the pattern by substituting Fe for Mn is linear.

[Josele]

Some time ago I discovered that my hübnerite specimen was magnetic I was thinking it had to be mostly ferberite until I was told that pure manganese hübnerite is intrinsically magnetic even without any quantity of iron.
Unfortunately the magnetic method is not valid to differentiate hübnerite from ferberite.

[Jordi Fabre]

[Jean Sendero]

[cascaillou]

Ferberite-hubnerite is a series. And "wolframite" is an ill-defined intermediate member of the series. Thus, as far as a field trip goes, I'd be more concerned about confirming that I indeed have a member of that series in my hands, rather than checking which side of the series.

Let's still mention that:
The more iron, the more opaque it is and the higher the specific gravity is.
Also, streak color is said to be greenish gray for huebnerite, and dark brown to black for Wolframite and Ferberite.