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Comment 2-24-2015. I'm a man on the street knowing nothing about the subject. In the Wikipedia articles for each mineral the formula for goethite is given as α-FeO(OH) and diaspore AlO(OH). The article for the latter says they are isomorphous.

Then you say, "In order to form isomorphous crystals two substances must have the same chemical formulation …"

Those aren't the same formula. For me, either your statement is wrong or you aren't explaining it properly.

JIm Luedke — Preceding unsigned comment added by Jimlue ( talk • contribs) 19:50, 24 February 2015 (UTC) reply