10 January 2011
Mystery rock with radiating crystals
Posted by Callan Bentley
Putting up the wavellite crystals on Saturday reminded me that I needed to show you this thing and ask you to tell me what the hell it is:
I got this from an amateur geologist rockhound dude in Maryland, who got it from a collection of rocks hoarded up by another rockhound. When the one rockhound died, his widow let my rockhound go through the collection and claim whatever he wanted. My rockhound had this piece (bigger then) in his backyard, and then offered it to me. Because I have a rock saw, I suggested that I slice it in half, and we each keep a piece. So that’s what we did. Now here’s the question: what is this, and how did it form?
There’s no fizzing, anywhere. The little orbs are yellow on one side, and orange in the middle, and red on the other side, and everywhere they are surrounded with radiating green crystals that are stockier (non-acicular) than the wavellite in the previous post. These extend a distance, and then the space in between these mineralogical hedgehogs are either tightly clustered, with a gap in between them (as at the bottom), or they are more widely spaced (as at the top), with the intervening space filled with a white/red/pink cryptocrystalline matrix that looks and feels like chert.
What the heck? Tell me what to think of this oddball. Here’s a closer look, with a ruler for scale:
Any idea what the crystal matrix is? My first thought for the orbs would be oolites because of the layered and spherical nature of them, but I’ve only ever seen oolites in limestone, I don’t know what they would be doing in crystal like that.
I would love to know if anybody has seen anything like this before! Very cool.
The matrix is hard, and it doesn’t fizz. That’s all I know. Can I test it in some way for you?
I’m trying to think of how the round things could have been somehow suspended (and dispersed pretty far apart like you noted) to allow the crystals to grow around them like that.
It’s kind of like the opposite of a geode–instead of crystals growing inside the rock, they nucleated outside the round things.
I would be interested in the hardness, I’m wondering if the crystals are quartz with a green impurity.
What about fluorite? I’m starting to think this is some kind of evaporite.
Not fluorite – too hard (>6.5 on the Mohs scale)
Right — good call, Laurie. It’s like a zillion little anti-geodes. That’s a good way to think of it.
Errmmm….I’m not a rock expert, but can I ask you something? Since wavellite is ‘crustal’ layer on aluminous metamorphic rock, could this rock be somewhat, another type of metamorphic rock? Pardon this silly question, I’m just an inexperienced graduate. The patterns just reminded me of seeing something of carbonaceous nature.
The wavellite in the previous post was an “encrustation” on the surface of the quartzite. It is a vein filling — not really a metamorphic “rock,”per se. The textures here, both in terms of the pisoliths/ooids and the surrounding green “spar” seen in some parts of the rock indeed remind one of carbonate (which is I think what you meant by “carbonaceous,” which means “full of carbon”), but ooids form on the bottom of the sea, and are thus pretty closely packed together, whereas these guys are pretty widely distributed in three dimensions.
And PS – there’s no such thing as a silly question! Thanks for asking it. Probably other people were wondering the same thing.
Thanks for clearing that up for me. Now that I read the definitions again, it did say that it forms under ‘hydrothermally’. I really need to hit the books back pronto. I can’s really observe much when I see it that way.If only I could observe the thin section of the thing. I could only tell that there are quartz-like spikes surrounding the ‘chert-like’ orangish ball thingie. This is totally beautiful. SInce it doesn’t fizz, I take it you meant by the acid test right?
Right — the “fizz” bit refers to the absence of a reaction with hydrochloric acid, HCl.
ok…I kind of go with Laurie but I’m seeing it in the simple igneous mineral formation sequencing view. If the ‘hedgehog’ radiating acicular crystals are that well-formed, it must’ve gone through slow cooling. But, in my experience just go as far. I was just reading something on carbonatite and it’s starting to give me ideas,but hopefully, I’m not being too shallow about this.
Rank amateur here. It looks like the little red things (see, technical) were pelleted at high speed into the crystal causing fracture. Since they’re red, I’m thinking pieces of iron meteor? What does the outside look like?
Not likely. The green “fractures” you see radiating out are actually the boundaries of crystals: solid masses which grew in that shape. This radiating pattern is usually interpreted as the green crystals nucleating on the surface of the red things, and then growing outward in all directions. The “outside” looks exactly the same — this pattern is uniform in two dimensions, and the thrid dimension shows the white-to-green pattern, and the yellow-to-orange-to-red pattern. What you see in these images is representative of the whole rock.
Callan, What is the hardness of the green radiating crystals? Also what does the uncut side of the rock look like?
iPhone photo of the other side: http://www.flickr.com/photos/[email protected]/5343444026/sizes/l/
I’ll check the hardness now… stay tuned.
The green mineral is harder than a streak plate… (>6.5)…
ahah! quartz!!! I’m starting to feel good about what I’m pondering
Callan, Never mind the question about the uncut side of the rock, missed the explanation in the previous post.
It looks like Ocean Jasper from Madagascar.
That really DOES look like it!
ok…. here is another amateur…..
the first thing that pop out to my mind is that the condition (like temperature) in which the rock was formed changed gradually as a result we have a crystal that developed….. differently???
for example, when magama cools down, the temperature favors one kind of mineral over another to crystalized first. but a sudden changed of temperature would favor another mineral to crystalized.
it is a nice sample!
I’ll be tunned to see who knows what it is.
Totally — Michael Popp called it. Check out this suite of images via Google.
Am glad to find out where this is from. We acquired some in a similar way a few years ago and it was always a starting point for discussion. I assume the mass is somehow related to volcanism like chalcedony. I guess diopside doesn’t fit with chalcedony. Am curious about the minerals and how the texture formed.
I posted the question and a link to your blog to our local Georgia Mineral Society. Jim Flora responded the same as Michael Popp and gave this description and link.
OCEAN JASPER : Marketing term for a spherulitic variety of chalcedony.
Orbicular jasper or Ocean jasper – from some Island off Madagascar
I’m glad our experts were so quick to identify this.
Pretty cool, right? The internet really fulfills my expectations some days… 🙂
Looks very much like this. And it seems that you got a very nice piece.
Still curious about the minerals and the mechanisms for formation
I’d chalk it up to something like this:
A silica-rich solution gets a few little nucleations in it. These little nubbins get sloshed around and coated with many layers of silica, with staining from small concentrations of impurities (the same sort of coloration that gives us chalcedony or the varieties of colored quartz today: the red variety is “jasper”). As the layers accumulate, the little spheres grow in size. Later, crystals of green-tinted quartz (?) grow outward from the spheres, nucleating on their surface and projecting outward, like skyscrapers poking off the round surface of the Earth. Eventually, these green crystals grow large enough that they interfere with their neighbors and close off small cavities (little void spaces in the green section), or they don’t grow large enough, and then chert (microcrystalline silica, white to pink in this sample) precipitates in the space between.
Amateur, you don’t know what an amateur is until you are able to step away from the subject and into a diverse subject. Odds are that the (salmon?), which layed those eggs died in the same moment that strange things occurred to its eggs. For a moment it appeared that the surrounds of the crystal structures held sixteen distinct sections; as are found in the various levels of our Sun from radiative zone to the segments in the corona; but some surrounds appear to hold more crystal segments, but with unclearness, or like a peeled orange.
So, do the circular portions not appear as biological cells C/W nucleus?
An ancient one.
No, these are not cellular structures — they are simply layered concretions, like a hailstone. Such structures, which geologists call “ooids” or “pisoliths” or “oncolites” depending on their size and shape, can be formed inorganically. They are not fossilized salmon eggs, though I can see why they evoke that impression. In fact, the term “ooid” was chosen because of this resemblance to fish roe.
These appear to be deposition in an open space filling that was partially occupied by quartz crystals. The quartz crystals first grew into the space in a radiating pattern from around the original walls of the open space. They then stopped growing and later a different phase of growth occurred that finished the filling of the open space with the concentric colored mineral. Since color usually means little when identifying minerals, it is unknown from a picture what it could be. But if I had to guess I would say it was some variety of cryptocrystalline quartz.
My 2 cents.
Thanks for chiming in. I find the idea that all the green quartz crystals were growing inward but then all stopped at the same point(s) which resulted in perfectly spherical void spaces an unlikely prospect. It strikes me as much more likely that the spheres are older (inclusions) with the green quartz coming later and encrusting them.
It is hard for me to see on your photo which came first, the spheres or the cavity. But, if the spheres are also encrusted then I see your argument. I played a little bit with the image in my graphics software to try and coax out some more detail but the resolution is too low. I realize you are restricted to smaller resolutions when posting on the web, but if you wanted to you could put a much higher resolution photo on a picture sharing site for downloading. Maybe AGU has such a feature?
Having said that, this structure reminded me of orbicular jasper I have seen before. If you are familiar with Google image search, then go there and put in “orbicular jasper” and you will get many results that look very close to what you have.
Yeah — that’s what it is. See the comment chain above. A reader named Michael Popp identified it as “ocean jasper,” an orbicular jasper from Madagascar.
I think “ocean jasper” is just a colloquial term. I am sure orbicular jasper can be found all over the world.
Do we know the green mineral is quartz?
Nope – that’s my working ID, subject to revision.
Ocean Jasper! Orbicular jasper is formed from rhyolite…can form anywhere conditions are right. It does look oolitic at first glance, but no ‘fizz’. What really interests me are what appear to be fractures contained within the innermost radial structures (at about the 6 mark). How might a spicule-like crystal growth fracture clear through then continue growing perfectly radial layers? Or is this some kind of compression fracture the was enough to affect only the inner crystal growth but stop at the ‘rind’? Seems unlikely…any hyptheses??
Those are saw-marks, I think — the trade-off with the super close view is that you guys get to see what a poor rock-polisher I really am.
My friend tells me that this is Ocean Jasper from Madagascar
A year and a half later than my January 2011 submit brings another suggestion, if one can consider that the eyeball appearance comes from electromagnetic energy, which is always created from activities deep underground and emit perpendicularly upward, then each of those circular devices could be a tubular collimated stream which has a central conductor system surrounded by magnetics. An active stream is composed of segments, if the energy is provided from an alternating source, but as a continuing stream while the energy continues to be supplied, just like a solar spicule in the chromosphere.
So, if a CS picked up liquid like rock material, (don’t laugh at my ineptitude), it would also be compressing that captured material as the transport of material consumes energy, thus lessening the stream’s dimensions. So, pressure changes the chemical process’ outcome, presenting a possible change to the mineral content. Another strange thing about CSs is that each segment is framed up on an electron signature circle of two concentric circles, with the inner circle having more pressure, which could account for the concentric circles. As to the radial effect, it is conceivable that a transfer of EM energy to the matter outside of the circles leaves traces of the energy passages in the radiating and enlarged areas around the eyeball appearance of the circles.
For a different view of rock tubes that could be slightly related to the beautiful polished rock, see p. 108 of May 2012 National Geographic magazine.
These aren’t tubes. They’re spheres.
Everyone who’s mentioned ocean jasper from Madagascar appears to be correct. Thanks for commenting, everyone.