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Magnetic LIZARDITE?
  
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Josele




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PostPosted: Jan 18, 2013 19:33    Post subject: Magnetic LIZARDITE?  

A Norwegian friend gave me this Lizardite / Hydrotalcite piece. I was checking magnetism trying to identify minor dark minerals scattered on the mass and they are very slightly magnetic. Surprisingly, I noted that pure Lizardite areas are really more magnetic than dark areas.

Can you help to explain this?
Perhaps is not Lizardite, but another Serpentine Group specie containing Fe?

Thanks for your comment.



liza1no.JPG
 Description:
Lizardite, Hydrotalcite and more.
Dypingdal Serpentine-magnesite deposit, Snarum, Modum, Buskerud, Norway.
8 x 6 x 4 cm
 Viewed:  10411 Time(s)

liza1no.JPG



htal1no.JPG
 Description:
Lizardite, Hydrotalcite and more.
Dypingdal Serpentine-magnesite deposit, Snarum, Modum, Buskerud, Norway.
8 x 6 x 4 cm

Reverse side. White bent fibrous Hydrotalcite with pearly lustre. Dark minerals are only very slighly magnetic, as hematite.
 Viewed:  10401 Time(s)

htal1no.JPG



liza2no.JPG
 Description:
Lizardite, Hydrotalcite and more.
Dypingdal Serpentine-magnesite deposit, Snarum, Modum, Buskerud, Norway.
8 x 6 x 4 cm

Neodymium magnet (∅6 x 3 mm) sticks to Lizardite strong enough to support his own weight.
 Viewed:  10420 Time(s)

liza2no.JPG



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cascaillou




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PostPosted: Jan 18, 2013 22:59    Post subject: Re: Magnetic LIZARDITE?  

It's likely that the greenish-yellow material is not the one responsible for the magnetic behaviour but rater the metallic luster material that is mixed/included in.
Basically, magnetic minerals are containing iron, nickel or manganese.
It is interesting to note that while few minerals respond to a ferrite magnet (the black kind you stick on the fridge), many will react to a neodymium magnet (much more powerful).
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GneissWare




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PostPosted: Jan 18, 2013 23:24    Post subject: Re: Magnetic LIZARDITE?  

This locality is well known for magnetite and hematite ps. after magnetite which is exposed by removal of the encompassing lizardite / hydrotalcite / other serpentine minerals. You are seeing the effects of hidden magnetite / hematite.
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prcantos
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PostPosted: Jan 19, 2013 03:29    Post subject: Re: Magnetic LIZARDITE?  

GneissWare wrote:
...You are seeing the effects of hidden magnetite / hematite.


All right. The processes of serpentinization of ultrabasic olivine-rich rocks isolate Fe from fayalite to generate iron oxides such magnetite, which impregnate the bulk rock and often cause notable magnetic properties and dark colour in the rock. Mg from forsterite remains in serpentine group minerals.

If you check your serpentinite rocks and serpentine minerals specimens, you will probably find that most of them are magnetic! (I mean your neodymiun magnet will be attracted by the samples). Mine are so.

Regards.

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Josele




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PostPosted: Jan 19, 2013 07:46    Post subject: Re: Magnetic LIZARDITE?  

You are right. Today I rechecked the sample and not all clean lizardite areas shows magnetic attraction. Some areas are completely inert. Then the magnetic Lizardite areas must have some magnetite under the surface.

Most of dark minerals in this sample shows very slight magnetism, being not possible to lift up the magnet. For my experience in magnetic minerals, I think most of dark stuff could be hematite. But some black points are strongly magnetic, as correspond to magnetite.

Thanks to all for your help.

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GneissWare




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PostPosted: Jan 19, 2013 10:41    Post subject: Re: Magnetic LIZARDITE?  

Here is an example of a specimen from this locality that has been cleaned to reveal the Hematite ps after Magnetite hiding under the serpentine minerals,,,


IMG_4686.jpg
 Description:
Hematite ( ps. Magnetite ) in Hydrotalcite and Lizardiite
Øvre Dypingdal Quarry, Snarum, Modum, Buskerud Fylke, Norway
89 x 64 x 51 mm
60 x 30 mm crystal
 Viewed:  10245 Time(s)

IMG_4686.jpg


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alfredo
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PostPosted: Jan 19, 2013 13:05    Post subject: Re: Magnetic LIZARDITE?  

Let's not forget that magnetism is not exclusively a property of iron-rich minerals. Some minerals with very little or no iron will also be quite strongly attracted to modern neodymium magnets: eg - hubnerite and rhodochrosite, even when these contain almost no Fe substituting for Mn. In other words, we cannot assume that a mineral is Fe-rich just because it is attracted to a strong magnet.
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Riccardo Modanesi




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PostPosted: Jan 19, 2013 15:26    Post subject: Re: Magnetic LIZARDITE?  

Hi to everybody!
However the metallic magnetite crystals are very sightable in this specimen, therefore I fully agree with Cascaillou and GneissWare when they say there is magnetite among the minerals compounding this specimen.
Greetings from Italy by Riccardo.


Josele wrote:
A Norwegian friend gave me this Lizardite / Hydrotalcite piece. I was checking magnetism trying to identify minor dark minerals scattered on the mass and they are very slightly magnetic. Surprisingly, I noted that pure Lizardite areas are really more magnetic than dark areas.

Can you help to explain this?
Perhaps is not Lizardite, but another Serpentine Group specie containing Fe?

Thanks for your comment.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Josele




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PostPosted: Jan 19, 2013 17:48    Post subject: Re: Magnetic LIZARDITE?  

alfredo wrote:
Let's not forget that magnetism is not exclusively a property of iron-rich minerals. ....

I knew some wolframates as Hübnerite are paramagnetic. Rhodochrosite is a surprise for me, thanks Alfredo.

Both minerals are manganese salts. I imagine magnetism of these minerals is due to Mn properties more than to combinated anions.

Thanks for your input.



p1090652.jpg
 Description:
Hübnerite
Huayllapon Mine, Pasto Bueno, Pallasca, Ancas, Peru.
4,5 x 2,5 x 2,5 cm
 Viewed:  10202 Time(s)

p1090652.jpg



P1100801.JPG
 Description:
Rhodochrosite
Hezhou, Guangxi Zhuang, China.
Main crystal: 2,5 x 1,5 x 1 cm
 Viewed:  10176 Time(s)

P1100801.JPG



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Pete Modreski
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PostPosted: Jan 19, 2013 23:03    Post subject: Re: Magnetic LIZARDITE?  

Those pictures are quite impressive! They point out very clearly how testing for magnetism with one of the modern rare-earth magnets is quite a different thing than with the traditional, much weaker magnets.
May I ask--does anyone have any advice as to what's an ideal size of a Nd-magnet to use for testing minerals, and perhaps, any suggestions of places to buy some? Just checking online, they seem to be available in a bewildering variety of sizes and shapes, most of which don't seem to handy for experimenting with minerals. I've been thinking for a long time that I should have one (or more) to examine minerals--I've never really had access to one, or known exactly where to buy one. Has anyone seen mineral dealers selling these along with other mineral-related equipment?
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Josele




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PostPosted: Jan 20, 2013 09:14    Post subject: Re: Magnetic LIZARDITE?  

Pete Modreski wrote:
... May I ask--does anyone have any advice as to what's an ideal size of a Nd-magnet to use for testing minerals, and perhaps, any suggestions of places to buy some? ...

Pete, yes, these magnets are surprisingly strong. I use a piece of a magnetic toy called Geomag, available in many toy stores.
Size of individual magnet is ∅6 x 3 mm. It weights 0,65 g and is able to pull up easily a half kilo piece of iron, more than 750 times his own weight.



P1100807.JPG
 Description:
At left can see a piece of Geomag toy. If you take out plastic envelopment, you will find a ∅5 x 20 mm inert iron cylinder with ∅6 x 3 mm neodymium magnets in both ends, as can see at right.
 Viewed:  10091 Time(s)

P1100807.JPG



P1100808.JPG
 Description:
To check minerals with a weak magnetism can do like this: leave one of these magnets standing on the edge on a flat and horizontal table, will be oriented instantly pointing to N - S with the axis through the center of its two circular faces. It's like a very fast compass.
To check light paramagnetic attractions, put the magnet on a table as explained and approach the mineral to make contact. Now try to drag the magnet pulling the mineral, not pushing. Thus, as the force required to roll the magnet is very small, even light attractions become evident.

Here checking an Epidote from Mali.
 Viewed:  10069 Time(s)

P1100808.JPG



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cascaillou




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PostPosted: Jan 20, 2013 20:27    Post subject: Re: Magnetic LIZARDITE?  

here's a website dedicated to gemstone magnetism: http://www.gemstonemagnetism.com
(link normalized by FMF)

It describes the testing procedure and the evaluation of the reaction intensity, and provides magnetic data for a lot of gems.

The magnet standardized size and strength for gem testing is a ½” x ½” (12.7 mm) cylinder, N-52 grade.
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Josele




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PostPosted: Jan 21, 2013 10:18    Post subject: Re: Magnetic LIZARDITE?  

cascaillou wrote:
here's a website dedicated to gemstone magnetism: http://www.gemstonemagnetism.com
(link normalized by FMF) ....

Cascaillou's link gives a very usefull method to identify minerals, with a floating system that can detect very weak attractions. Very thanks for share it here.



P1100811.JPG
 Description:
Almost all tourmalines in my collection are more or less magnetic, this rubellite from Myanmar is the only one that do not shows attraction to magnet.
 Viewed:  9894 Time(s)

P1100811.JPG



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