What is the composition and origin of this rock found in Israel?

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Discussion Overview

The discussion centers around the composition and origin of a rock found in Israel, identified as a "hammerstone" or pounder. Participants explore its geological characteristics, potential mineral content, and the implications of its shape and condition, considering both local geological processes and human usage.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests the rock may be granite with k-feldspar, while others propose it could be quartzite based on its fractured surface.
  • There is a suggestion to conduct destructive analysis on similar local specimens to better understand the rock's composition.
  • Some participants note the importance of examining the rock's interior, as the weathered exterior may not provide sufficient information.
  • One participant raises the question of whether the rock is magnetic, prompting others to consider the presence of magnetic materials like magnetite or iron oxide.
  • Another participant hypothesizes that the rock may have been used to prepare red ochre, indicating a potential historical use.
  • Discussions include the implications of the rock's shape, with some suggesting it may indicate alluvial processes or human modification.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the rock's composition and origin, with no consensus reached on its exact nature or the processes that formed it. Multiple competing views remain regarding its geological characteristics and historical significance.

Contextual Notes

Participants note the limitations of the discussion, including the lack of interior examination of the rock and the need for further analysis to clarify its composition and history.

wilhen
https://drive.google.com/file/d/0B6vFDqtp6QNEOW9CeUFYOWRGczA/view?usp=sharing The pictures in this post are of a "hammerstone," or pounder. It was found next to a large lower grinder (metate, quern, whatever term you prefer). It is 11 cm high and 13 cm wide. It most likely cracked from heat exposure incident to the destruction of the house it was found in. The site is located between Tel Aviv and Jerusalem, Israel. A friend suggested it might be granite and the red areas exposed from the chipped cortex might be k-feldspar. I was wondering if you had other suggestions.
https://drive.google.com/open?id=0B6vFDqtp6QNEOW9CeUFYOWRGczA
https://drive.google.com/open?id=0B6vFDqtp6QNEUzJVMG9Gd1FPSzQ
 
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Some points:
This has an accession number on it so you have to treat it carefully.

Showing the inside of the rock ball will help - the weathered rind is not very enlightening. The cracks appear to allow a full cross-sectional view.

People do not want to lug large rocks around so the likelihood is that the rock is local or an accidental, so other specimens probably lurk in the locale. And you can have a mineralogist do destructive analysis on those other specimens if needed. e.g., acid tests or sections for microscopy.

If the shape is not man-made then it implies alluvial processes were at work - like violent stream flows or glaciation.
 
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Just a hunch - but is it magnetic ?
 
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jim mcnamara said:
Some points:
This has an accession number on it so you have to treat it carefully.

Showing the inside of the rock ball will help - the weathered rind is not very enlightening. The cracks appear to allow a full cross-sectional view.

People do not want to lug large rocks around so the likelihood is that the rock is local or an accidental, so other specimens probably lurk in the locale. And you can have a mineralogist do destructive analysis on those other specimens if needed. e.g., acid tests or sections for microscopy.

If the shape is not man-made then it implies alluvial processes were at work - like violent stream flows or glaciation.
Thanks, Jim. The site directors gave me permission to research this piece, and without specific context I thought it would be safe to put on a forum. Unfortunately, I didn't get a picture of the rock interior. We're confident the rock is a tool because of pecking on the bottom side, not shown in the photographs.
 
Nidum said:
Just a hunch - but is it magnetic ?
I don't know. I never placed a magnet near it.
 
The fractured surface of the rock looks to me a bit like a quartzite.

If you look closely at the bottom of pix 1 you will see some lines or curves that appear to be variations in the rock. I suspect they were fossil shell CaCO3 fragments that were dissolved in the metamorphic process by silicic acid, then replaced with silica.

The parallel cracks suggest either historical weaknesses due to bedding, or unloading cracks formed during uplift and approach to the surface.

Rotate the rock near a magnetic compass to see if magnetic material is present. Red iron oxide haematite is not magnetic, black magnetite is magnetic.

The red surface may be iron oxide produced by weathering in the soil. It appears to have stained the cracks in the rock and the weathered crust.

Maybe the rock was used to prepare red ochre and retained some material.
 

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