Michael V said:
Are you going to tell me about those rock photos you put up?
OK, here are some more photos.
He did say identifying a rock from pictures is unlikely.
buffy said:
He did say identifying a rock from pictures is unlikely.
Yes, I think you’re wasting your time with these extra pictures. Better to show it to a geo in real life.
buffy said:
He did say identifying a rock from pictures is unlikely.
Yes but he also asked me for more info. It is green with a lot of what look to be invertebrates or inclusions of calciferous material.
It could be a form of Chalcedony or Chrysoprase but the inclusions are strange.
dv said:
buffy said:
He did say identifying a rock from pictures is unlikely.
Yes, I think you’re wasting your time with these extra pictures. Better to show it to a geo in real life.
It would cost a motza to send in the mail and it doesn’t belong to me. There’s plenty of time though to show it to several geologists or gemnoloists.
Where was it found?
What other rocks were in the immediate vicinity?
What other rocks were in the general area?
How hard are the various minerals? (A sharp pocket knife will easily scratch calcite, but won’t scratch quartz, feldspar or chalcedony.)
Is that yellowish groundmass made of interlocking grains?
Is the yellowish groundmass soft or hard (or indeed a bit of each)?
Michael V said:
Where was it found?What other rocks were in the immediate vicinity?
What other rocks were in the general area?
How hard are the various minerals? (A sharp pocket knife will easily scratch calcite, but won’t scratch quartz, feldspar or chalcedony.)
Is that yellowish groundmass made of interlocking grains?
Is the yellowish groundmass soft or hard (or indeed a bit of each)?
It is said to come from Cairns. I’ll try to verify.
Hardness seems to be the issue in that the inclusions are easily dug out with the point of a S/S knife. The green stuff can be marked with the same knife point but it is definitely harder, not more than 4.5 to 5 maybe.
The mass appears to be small granules of some conglomerate type, likely some calcite type. the smaller particles are harder than the general mass.
roughbarked said:
Michael V said:
Where was it found?What other rocks were in the immediate vicinity?
What other rocks were in the general area?
How hard are the various minerals? (A sharp pocket knife will easily scratch calcite, but won’t scratch quartz, feldspar or chalcedony.)
Is that yellowish groundmass made of interlocking grains?
Is the yellowish groundmass soft or hard (or indeed a bit of each)?
It is said to come from Cairns. I’ll try to verify.
Hardness seems to be the issue in that the inclusions are easily dug out with the point of a S/S knife. The green stuff can be marked with the same knife point but it is definitely harder, not more than 4.5 to 5 maybe.
The mass appears to be small granules of some conglomerate type, likely some calcite type. the smaller particles are harder than the general mass.
Some of those structures look like geodes, particularly those near the top half of this picture. That’s consistent with the hardness, too.
But the elongated shape in the bottom of this picture looks more like a fossil.
And some other shapes look to have been fractured like a breccia.
So in summary, I haven’t really got a clue. If I had to guess, I’d say it was a type of marble. ie. limestone that’s been subjected to fracturing from a little shearing, a lot of heat, and deposition of silica from water penetration.
It reminds me a little of the Agate Creek Thunderegg Rhyolite.
In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
roughbarked said:
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
roughbarked said:
roughbarked said:
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
How about Jasper Rhyolite Agate?
roughbarked said:
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
I take it we are talking about the nodules.
The central mineral?
Or the outside mineral?
Michael V said:
roughbarked said:
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
I take it we are talking about the nodules.
The central mineral?
Or the outside mineral?
The green mass.
The nodules are harder than the crumble they are held in. Difficult to scratch because they are small.
roughbarked said:
roughbarked said:
Michael V said:
It reminds me a little of the Agate Creek Thunderegg Rhyolite.In this rhyolite, some bits of the glassy fraction (with the help of warm groundwater) spontaneously devitrified into roughly concentric nodules of chalcedony surrounded by clay. In some places the nodules reach 4 cm diameter. I’m guessing that your rock’s nodules reach 5 mm or so.
Hardness is not the ability to dig a mineral out of a rock.
Hardness is a scratch test; does the mineral scratch or not when challenged by an object of known hardness.
Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
Opal varies in hardness depending on how hydrated it is.
Michael V said:
roughbarked said:
roughbarked said:Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
Opal varies in hardness depending on how hydrated it is.
Correct. Which is why I mentioned good crystal. It is hard enough to require a grinding compound with a hardness greater than 7.
roughbarked said:
roughbarked said:
roughbarked said:Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
How about Jasper Rhyolite Agate?
Seems that that is a local (non-geological) name.
roughbarked said:
Michael V said:
roughbarked said:Yes. I can make a mark with the pointy end of a stainless steel knife. It ain’t much of a mark but a scratch it is. So it is not as hard as steel.
I take it we are talking about the nodules.
The central mineral?
Or the outside mineral?
The green mass.
The nodules are harder than the crumble they are held in. Difficult to scratch because they are small.
You might need to put an arrow onto a photo to show me “the green mass”.
My colour vision is not particularly brilliant.
Michael V said:
roughbarked said:
roughbarked said:
It isn’t as hard as good crystal opal, with the same knife. I’d guess at somewhere between 4 and 5 on the scale.
How about Jasper Rhyolite Agate?
Seems that that is a local (non-geological) name.
Thought as much. thanks.
Michael V said:
roughbarked said:
Michael V said:I take it we are talking about the nodules.
The central mineral?
Or the outside mineral?
The green mass.
The nodules are harder than the crumble they are held in. Difficult to scratch because they are small.
You might need to put an arrow onto a photo to show me “the green mass”.
My colour vision is not particularly brilliant.
OK you mentioned yellow mass earlier on. Maybe you are seeing the green as closer to yellow?
roughbarked said:
Michael V said:
roughbarked said:The green mass.
The nodules are harder than the crumble they are held in. Difficult to scratch because they are small.
You might need to put an arrow onto a photo to show me “the green mass”.
My colour vision is not particularly brilliant.
OK you mentioned yellow mass earlier on. Maybe you are seeing the green as closer to yellow?
I mentioned the yellow groundmass.
As to what I see, it is what it is. It may be different to you, but I can’t quantify that difference in any meaningful way.
If you use the BoM website : http://www.bom.gov.au you might notice that it is not secure due to the fact that it does not support SSL and cannot be accessed using the https protocol.
But, the entire site is securely mirrored at https://reg.bom.gov.au
Should you care? Maybe.
fsm said:
If you use the BoM website : http://www.bom.gov.au you might notice that it is not secure due to the fact that it does not support SSL and cannot be accessed using the https protocol.But, the entire site is securely mirrored at https://reg.bom.gov.au
Should you care? Maybe.
Probably in the wrong thread.
Michael V said:
roughbarked said:
Michael V said:You might need to put an arrow onto a photo to show me “the green mass”.
My colour vision is not particularly brilliant.
OK you mentioned yellow mass earlier on. Maybe you are seeing the green as closer to yellow?
I mentioned the yellow groundmass.
As to what I see, it is what it is. It may be different to you, but I can’t quantify that difference in any meaningful way.
I maked one part of the green areas
All the areas between the white intrusions are green.
roughbarked said:
Michael V said:
roughbarked said:OK you mentioned yellow mass earlier on. Maybe you are seeing the green as closer to yellow?
I mentioned the yellow groundmass.
As to what I see, it is what it is. It may be different to you, but I can’t quantify that difference in any meaningful way.
I maked one part of the green areas
All the areas between the white intrusions are green.
The light for taking photos has been poor of late so the green may appear grey/green to some eyes.
roughbarked said:
Michael V said:
roughbarked said:OK you mentioned yellow mass earlier on. Maybe you are seeing the green as closer to yellow?
I mentioned the yellow groundmass.
As to what I see, it is what it is. It may be different to you, but I can’t quantify that difference in any meaningful way.
I maked one part of the green areas
All the areas between the white intrusions are green.
Thanks. That’s the groundmass.
The other bits are the (roughly concentric, seemingly two mineral) nodules.
roughbarked said:
roughbarked said:
Michael V said:I mentioned the yellow groundmass.
As to what I see, it is what it is. It may be different to you, but I can’t quantify that difference in any meaningful way.
I maked one part of the green areas
All the areas between the white intrusions are green.
The light for taking photos has been poor of late so the green may appear grey/green to some eyes.
No problems. Having the arrow really helps.
The owner of the rock had his locations mixed up. It came from Cooktown rather than Cairns. His sister picked it up in a creek at Cooktown. He had it cut in half so they had a piece each. Unfortunately he laquered the surface where it was cut which may cause issues with checking lustre.
