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please help identify this rock. it is heavier than most. dark brown color. picture is shown with streak test. found in Philadelphia pa. at home demolition site. crystals seem to be different type and color some look black and some clear. some places look bubbley like it was melted. couldn't scratch with a knife. enter image description here

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  • $\begingroup$ Black's bubbles on 3rd picture looks like botroidal iron oxydes. Hemathite or goethite and amorfous iron oxydes $\endgroup$ – Universal_learner Oct 6 '18 at 18:20
  • $\begingroup$ Does all the rock leave a redish streak or some zones a yellowish/brownsh one? $\endgroup$ – Universal_learner Oct 6 '18 at 18:59
  • $\begingroup$ Red in all areas. $\endgroup$ – Leeb Oct 6 '18 at 19:12
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    $\begingroup$ What material can I use to test density? $\endgroup$ – Leeb Oct 6 '18 at 19:17
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    $\begingroup$ Ok I came up with a density of 4.95 $\endgroup$ – Leeb Oct 13 '18 at 15:49
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The texture of the third picture and the streak carries to clasify the zone of the dark bubbles as "botroydal hematite".

Hematite is an iron oxyde that leaves a redish streak.

It is common at enrichment supergenic deposits forming the top crust of the ore, named gossan.

It is found at some mines of Philadelphia.


It appears sometimes mixed with other iron oxydes but the homogenous streak you noticed make me think your piece is mainly composed by hematite.

A density test would clarify this. If it has not a lot of other iron oxydes it will be close to 5.3 g/cm3, if not it could fall easily to 4 g/cm3or so.


Upgraded: You measured a density of 4.95 g/cm3. We much apreciate your effort providing the data we asked.

Your piece is composed by hematite with some impurities.

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