FMF - Friends of Minerals Forum, discussion and message board

[convento]

hello, bring this rock from a mountain in north portugal.liked it because of the colours, diferent from the others near it.
Just curious to know what is it, as i do not understand nothing from rocks and minerals. so any help would be good, as it's my first rock. thank you!

[Matt_Zukowski]

It looks like some sort of cryptocrystalline quartz, but you don't really know unless you do some tests. You can find information about tests you might do here: "What is this? / Where is it from?"

I think the things people would most like to know to help you are:

1) Does it fizz? Carbonate rocks fizz when you put a dilute acid on them as the reaction of an acid with a carbonate produces CO2 gas. Dilute (10%) hydrochloric acid works best for a fizz test but even a weaker acid like vinegar can work - for vinegar it is best if you grind up the rock into a powder and put vinegar, especially heated vinegar, on the powder.

2) How hard is it? Minerals differ in their hardness so knowing what the hardness is a of particular specimen can help identify it. Look at the link cited above for info on hardness testing but basically you try to scratch your unknown with things of various hardness - things that scratch the unknown are harder than the unknown and things that are less hard than the unknown are scratched *by* the unknown.

3) What kind of cleavage does it have? With something like this i would like to break it open to see how it fractures. Fracture patterns can have some diagnostic value.