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I found this rock along the shoreline of Lake Ontario in the town of Ajax. It stood out from the smooth pebbles surrounding it and at fist glance I thought it was a piece of concrete. When I picked it up I found it to be surprisingly heavy. The rock measures 100mm x 50mm (4"x2") and weighs 1kg (2.2lbs).enter image description here

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closed as off-topic by Universal_learner, arkaia, Fred, Peter Jansson, Jan Doggen Jul 15 at 17:53

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  • "Please review our rock identification guidelines to provide the missing information so that your question is both answerable and useful to new users." – Universal_learner, arkaia, Fred, Peter Jansson, Jan Doggen
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Please read this, give more info, and add a photo under daylight. $\endgroup$ – Jan Doggen Nov 10 '16 at 12:28
  • $\begingroup$ You could do a displacement test to figure out its volume, from which you could calculate its density. Also, try seeing if a magnet sticks to it. $\endgroup$ – Spencer Dec 10 '16 at 21:06
  • $\begingroup$ There are two main 'zones' in your sample: resistant tan irregular shapes, and recessive areas that are slightly more orange. Look at these both very carefully: can you see small (<0.5mm) rounded grains? Can you please scratch a nail across both zones and post a picture? Can you find some 10℅ hydrochloric acid (eg from a high school chemistry teacher) and see if either zone fizzes? $\endgroup$ – Shawn Dec 20 '16 at 19:15
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You don't give the thickness, and with such a rough shape it is difficult to estimate the specific gravity. However, as a rough estimate it seems to have an SG of about 4 to 5.

It is most probably Goethite, an oxy-hydroxide of iron. The colour is exactly right for this mineral, but the density seems too high. The SG of Goethite is variable but generally <4. Try testing it's exact SG. If it really is 4 to 5 then I suspect it has an iron core, in which case it is a weathered and eroded scrap of man-made iron. It doesn't look like a weathered iron meteorite.

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