A very puzzling rock or a pallasite / mesmosiderite or a nothing burger

[malcolmh]

TL;DR Summary

Background

I recently showed an old friend, who graduated with a First from Cambridge in Geology back in the early seventies, a rock I found almost forty years ago.

He was intrigued.

(i) A bulk density test gave an approximate value of 4.5kg/m3.

(ii) The rock is ferromagnetic. It measures 16cm x 14cm at widest points and weighs 4.5kg. The bulk density would appear to rule out either slag.

(iii) It would appear to have a fusion crack which stretches across one face and another small crack to one edge.

(iv) There is the appearance of nickel flecks spread randomly across the surface. Some may be crystalline silica and others gold. Depends upon the angle of view.

(v) The vesicles would appear to be on the fusion crust and not on the interior.

The only possible alternative would seem to be magnetite which has been mined in Yorkshire where I live but the bulk density does not match.

Were magnetite to be ruled out, this rock could possibly be a pallisite or mesosiderite as per Meteoritics & Planetary Science, vol. 38, no. 8, p.1161-1180 based on its bulk density but I am sure that is far from sufficient for identification purposes.

Scarcely credible I know so my expectations are at a very low level and do apologise in advance if this is a waste of your valuable time!

I am attaching some photographs.

I would be most grateful for your initial thoughts if time allows.

Kind regards

Malcolm

 

[DaveE]

(i) A bulk density test gave an approximate value of 4.5kg/m3.

Seems way too light, is this correct? You meant gm/cm³?
Iron density is 7800 kg/m³
Glass density is 2500 kg/m³
Balsa Wood is 100- 250 kg/m³

Maybe @davenn can help?

 

[Baluncore]

I would be most grateful for your initial thoughts if time allows.

Where exactly did you find it ?
Google Earth, Latitude and Longitude ?
What situation? In a stream bed, the side of a volcano, or on the front lawn ?

 

[malcolmh]

Hi there - perversely enough in a nearby field.

Lat 53.841965

Long -0.435093

There have been a very very few meteorites in this part of the world and am far from suggesting it is however the bulk density does puzzle me. Way too high for slag / magnetite / haematite.

Quite bizarre...

 

[malcolmh]

Seems way to light, is this correct? You meant gm/cm³?
Iron density is 7800 kg/m³
Glass density is 2500 kg/m³
Balsa Wood is 100- 250 kg/m³

Maybe @davenn can help?

Hi, many thanks for the reply.

The bulk destiny is as given.

It's 0.0045000000000000005gm/cm3

or

4.5kg/m3

There is a difference between density & bulk destiny. Bulk density is determined by the its displacement in water.

 

[berkeman]

4.5kg/m3

Looks like you've found a dirty piece of Aerogel. Maybe it fell off one of the old Space Shuttles during reentry...

https://en.wikipedia.org/wiki/Aerogel

 

[malcolmh]

I doubt whether it would have left earth with that weight.

 

[DaveE]

The bulk destiny is as given.

It's 0.0045000000000000005gm/cm3

or

4.5kg/m3

There is a difference between density & bulk destiny. Bulk density is determined by the its displacement in water.

That is an interesting rock! 10-20% the bulk density of balsa wood!

 

[Baluncore]

It measures 16cm x 14cm at widest points and weighs 4.5kg.

If I guess, the other dimension is 10 cm.
16 * 14 * 10 = 2240 cc.
Then density is; 4500 g / 2240 cc = 2.01 g/cc = 2.01 tonne/m3.
That puts it in the slag category.

 

[DaveE]

A bulk density test gave an approximate value of 4.5kg/m3.

The bulk destiny is as given.

It's 0.0045000000000000005gm/cm3

Awesome lab skills there! I think you can remove the "approximate" in the first post.

Alternatively, you might have misunderstood significant figures. Most people's calculators are way to precise for everyday use.

Also, just out of curiosity, does in float in water?

 

[Baluncore]

That puts it in the slag category.

Further to my suggestion that it might be industrial slag ...

Article in Archaeological Journal · January 2011.
Title: Iron, Landscape and Power in Iron Age East Yorkshire.
By: Peter Halkon with a contribution by David Starley.

Extract ....
"Further downstream at Thearne, near Beverley (Campbell 2007; 2008), large slag blocks similar to those from Moore’s Farm have been identified on a spit of land protruding eastwards towards the River Hull. There are bog ore deposits here and, in the early summer of 2009, tree planting resulted in the discovery of the remains of a furnace (Illus. 9). "
https://www.researchgate.net/profil...cape-and-Power-in-Iron-Age-East-Yorkshire.pdf

 

[malcolmh]

Indeed it would (and many thanks for the kind reply). My question remains however is that industrial slag does not have the same bulk density nor does it account for gold flecks on this 'rock' which would surely have melted off in the furnace?

Any thoughts?

 

[Baluncore]

My question remains however is that industrial slag does not have the same bulk density nor does it account for gold flecks on this 'rock' which would surely have melted off in the furnace?

I like to get closer to the sample before coming to any geological conclusion. The sample is a bit hard to examine, with me now being on the other side of the Earth.

I don't think it is the remains of a cannonball, left over from the dispute between the Roses.

It could be an iron concretion from a bog iron deposit, that was maybe roasted, and then rejected as having insufficient value to justify the firewood and charcoal required.

It may be very old slag from the iron making process. Look for other examples in the district for comparison.

The surface flecks could be flux, or from the area near the kiln, or from the place where the concretion grew in the bog.

We are talking of a 2000+ year-old iron-age technology here. Your sample may have travelled like the ball in a pinball machine during that time. You can never tell how many times it might have been picked up and moved.

I see the area is too boggy for stone walls, so has hedges. Any rocks that surface during cultivation would be thrown towards, and under a hedge.

A good way to sample local geology is to look at field walls, and lowly farm buildings, since they are built from field rocks, found for free.

There has been a glaciation to contaminate the surface geology, higher sea levels, and then flat boggy country, so I expect surface rocks will be rare.

Your rock has almost certainly been pre-loved by a hundred generations.
You are not that different.

 

[Vanadium 50]

A rock with a density of 4.5 (I'm ignoring the "aerogel"typo) and a mass of 4.5 kg has a volume of 1000 cc. If two sides are 16 and 14, the other one is about 4-1/2. It's hard to tell from the photographs, but the rock looks rounder than that.

If the flecks are silica, it's not a meteorite.

Meteorites fall in England at the same rate as everywhere else.

To a very good approximation, the answer to the question "Is this a meteorite" is always "no". Most rocks, even funny-looking ones, did not come from the sky.

 

[Baluncore]

A rock with a density of 4.5 (I'm ignoring the "aerogel"typo) and a mass of 4.5 kg has a volume of 1000 cc. If two sides are 16 and 14, the other one is about 4-1/2. It's hard to tell from the photographs, but the rock looks rounder than that.

We know the rock is not flat, and that it is rounded to some extent. We can compromise by assuming the missing dimension is smaller by about the same amount as the first two differ. 16 cm, 14 cm, about 12 cm.
So, I model the rock as a spherical cow, with a diameter of 14 cm.
The volume = 1437 cc.
The given weight = 4500 g.
The density is therefore; 4500 / 1437 = 3.13 g/cc.

Bog iron contains; Limonite which has a density range of 2.7 to 4.3 g/cc.

https://en.wikipedia.org/wiki/Bog_iron
"Iron in the ore is reduced to a spongy iron bloom that stays in the upper part of the furnace while the undesirable elements stream downwards as slag. Smelting with a bloomery furnace often results in between 10 and 20 mass percent Fe being reduced to iron bloom, while the rest is transferred into the slag."

That all suggests you have an Iron Age ball of slag. I guess, about 2500 years old. It was left in the bottom of a primitive slag-pit furnace. It has remained near the surface due to land cultivation and soil erosion.

 

[malcolmh]

Many thanks for the kind reply.

(i) For an object to be slag, it is a necessary condition that its bulk density will be in the range of 1050 to 1375 kg/m3. If it falls above or below, it's simply something else.

(ii) We also know that it simply cannot be a terrestrial rock based on its bulk density. For it to be a terrestrial rock, it is a necessary condition that it must be in the range of 1600 kg/m3 (sediments) and 3500 kg/m3 (gabbro).

Again. If it falls above or below, it's simply something else.

(iii) Lastly, we know that it is a necessary condition that a pallasite or mesosiderite must be approx 4.5kg/m3. That does not mean that it is a stony iron I willingly accept.

Whilst it's a necessary condition, it's not a necessary & sufficient condition. Other tests are clearly required. It is however a necessary condition.

I'm simply asking for some scientific curiosity.

Items (i) and (ii) negate it being either slag or terrestrial. There is no amount of boosting slag with metal of such high density to take it to 4.5kg/m3. I have searched & searched for days but nothing.

 

[Vanadium 50]

Your mass, density and dimensions do not form a consistent set. I believe the density is closer to 3, as @Baluncore estimated, than 4.5.

I am not a slag expert, but doubt that it falls into such a narrow range. Your necessary condition most likely is not.

Your density "necessary condition" for terrestrial rocks is certainly not the case. Magnetitie, for example, has a density around 5.

 

[malcolmh]

Thank you for your kind reply. I am referring to bulk density.

experimental magnetite powder particle sizes range from 0.01 to 0.045 mm, the real density of magnetite powder is about 5000 kg/m 3 and the bulk density is about 2400 kg/m 3 .

 

[malcolmh]

I should state that the bulk density was measured by displacement of the item in water. I hasten to add, alas I'm not a physicist but I think I got that test correct.

 

[Baluncore]

I have searched & searched for days but nothing.

If you eliminate possibilities based on a "necessary condition", you must reference how you define that "necessary condition". You must also accurately measure that parameter for your sample.

Once you have wrongly eliminated what it really is, you will search & search for days, but find nothing. You must take greater care to avoid eliminating reality.

(ii) We also know that it simply cannot be a terrestrial rock based on its bulk density. For it to be a terrestrial rock, it is a necessary condition that it must be in the range of 1600 kg/m3 (sediments) and 3500 kg/m3 (gabbro).

Bog iron ore is limonite, it has a density of from 2.7 to 4.3 g/cc.
Hematite, an important mineral used as iron ore, has a density of 5.3 g/cc.

When, where, and how, was the density of your sample measured?
Your density claim of 4.5 kg/m3 is impossible. You must realise that is corrupt and take more care of the detail. Air at sea level has a density of about 1.3 kg/m3.

I assume that, if your sample density was measured and quoted as 4.5, the units would be 4.5 tonne/m3 = 4.5 kg/litre = 4.5 g/cc = 4.5 times the density of water.

It measures 16cm x 14cm at widest points and weighs 4.5kg.

The dimensions of the object are incomplete. How deep is it?
The volume is not specified.
What is the exact weight, accurate to the gram.

There is no amount of boosting slag with metal of such high density to take it to 4.5kg/m3.

Surely you mean 4500 kg/m3 = 4.5 g/cc.
Iron metal has a density of about 7.8 g/cc. With poor iron extraction, in an Iron Age furnace, the slag is expected to remain high in iron content. Indeed, because the ore is reduced by the charcoal, the weight percentage of iron in the slag, can be higher than in the original bog iron ore that was from 2.7 to 4.3 g/cc.

Modern furnaces recover a much greater percentage of iron from ore. The density of modern slag is therefore irrelevant. Iron Age slag is denser than any slag produced now. Early furnaces, that failed to complete, would have produced a high density lump in the pit. That would need to be crushed fine, and mixed with more charcoal to be re-smelted. It might be easier to abandon the failed lump, dig more peat, find more bog iron, because limonite is easier to process. A failed smelt may explain the origin of your sample.

Iron Age slag fits the profile better than any meteorite. The sample comes from a region known as a centre for primitive Iron Age furnaces and slag.

 

[malcolmh]

Most helpful - I shall go away and ponder.