Any Ideas?

[AussieMe]

This was found at Tennant Creek, Northern Territory, Australia.

The crystals are deep red in colour.

One side of the rock is green ( hard to see in the picture).

[Jeff McClendon]

My first thought was realgar and orpiment. If that is true be careful. Those are ores of arsenic sulphide.

[Geologyhound]

I concur.  Realgar and orpiment deposits tend to easily stir up dust when handled.  You don’t want to breathe it.  Handle with care.

In addition, the grey material with cubic crystals looks like galena - which is lead sulfide.

Nice little crystal deposits though.

[AussieMe]

The photos don’t really show the colour of the crystals very well. They are actually deep red in colour. And having looked up realgar and orpiment which states bright red and bright orange I would say that it isn’t that. I cleaned the sample in water and the green side of the rock seems to be becoming more green in colour which makes me think copper?

[jasong]

Streak test those crystals. 

Looks to me like a mishmash (ore, if you prefer). Something like an altered chlorite or greenschist for the gangue maybe, the colors seem congruent with hematite and limonite staining. Crystals my first guess would be pseudomorphs. Hex being either hematite coated quartz, or something after quartz. Cubics being hematite after pyrite/magnetite. 

Other minerals like chalcocite, sphalerite, etc readily form pseudomorphs after things like galena or whatever, if there are other metal ions available, so the mishmash can be even more complex to ID just from a photo as some of them can be cubics too or any shape really as a result. So in these cases, you really need to research the mineralogy of the specific area to get a good idea what things might be, and that would be up to you to do. But my first thought looking at it is some sort of mishmash ore, and since a lot of mineralized zones in Australia are old greenstone belts, greenstone of some sort would be my first thought for gangue rock.

Almost looks like an eclogite, but I don't think it is, still check and see if that kind of thing is found there maybe?

Everything I've said is 100% guess.

[Geologyhound]

Bear in mind also, there is some variability in visual color of many crystal species (streak color is a different issue).  Also, the color of a translucent or transparent crystal inside a vug while the crystal is sitting on a host rock will appear to be darker than if the crystal is all by itself with a light all around it.

The reddish crystals are hard to make out much detail in the pictures. Are the reddish crystals more in the form of pillars or prisms, or more in the form of multi faceted balls?