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i found this stone on the east coast of south island in New Zealand, it's 200 grams and very hard,i used a metal file on it and it left steel residue on the stone.

stone is brown with inclusions that look like crystal and dark speks.

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  • $\begingroup$ you need to add some more details please take a look here earthscience.meta.stackexchange.com/questions/124/… $\endgroup$ – trond hansen Mar 12 at 6:56
  • $\begingroup$ your comment to go and see wot to add makes no sense to me as half of what i said in the original post didnt show.its a brown stone/rock heavy for its size brown shiny smoth with what look like small crystals and dark spots that look burnt.if you need information please ask in a language a slow learner with head trauma can understand ,thankyou. $\endgroup$ – Irving Walker Mar 12 at 7:55
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This is a nice example of a volcanic rock, probably an andesite or something related.

The white crystals are plagioclase. The darker spots could be pyroxene, but I'm not sure.

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  • $\begingroup$ Gimelist, you must have been formulating your response as I was. I thought the red material looked coarsely crystalline which makes me consider the plutonic rocks. If examination of the rock show fine crystal structure on the red material then an andesite or rhyolite could be a possibility. $\endgroup$ – Friddy Mar 13 at 0:13
  • $\begingroup$ @Friddy the plag is perfectly euhedral. You don't get that in plutonic rocks. The red stuff has the some colour of (some) K-feldspars, but you don't see any crystals. I'd expect to see some cleavage or zoning or crystal shape, but there's nothing. This looks like a textbook example of a volcanic rock. $\endgroup$ – Gimelist Mar 13 at 11:12
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This answer is more of a guess, this is not my main area of interest.

The uniform crystal structure showing no layering leads me to believe that this is an igneous plutonic rock, a rock that formed from magma under the surface. The red matrix (the majority of rock) I am guessing is a type of K Feldspar (Alkaline Feldspar). I suggest this because K Feldspar typically appears white to brick read in colour. The milky white crystals are likely quartz. Feldspar is about 6 on Mohs hardness scale which is hard enough to scatch some metal but I would suspect a file might be harder. Quartz is 7 on the hardness scale and should scratch most steels. If the matrix is K Feldspar then I would say the rock is something like a Quartz alkali feldspar syenite (mostly feldspar with some quartz).

An alternative is that the red mineral is the quartz, I haven't seen quartz that red, in which case your rock would be closer to a simple granite or a granitoid. The alternative fits the scratching the file better but doesn't fit the color all that well.

Hopefully, someone with more knowledge will also answer. In the meantime, besides searching granites and quartz and feldspar on the web you may also encounter the QABF diagram found here.

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  • $\begingroup$ Thanks for your help guys appreciate your response. $\endgroup$ – Irving Walker Mar 13 at 16:30

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