Re: Maybe hematite flakes in this rock?

Dear Susie, I think you may get several replies to your pictures of this rock, and I think they will all agree on what it is. This is a quite typical-looking igneous rock; it’s what we would call an “intermediate composition” igneous rock, something like an andesite–not so dark and iron-rich as basalt, and not so light and silica-rich as rhyolite. The white crystals you see in it are feldspar, and the black ones are an iron-containing silicate mineral, probably either augite (a pyroxene mineral) or hornblende (an amphibole mineral). The rock probably contains just trace amounts of magnetite (iron oxide, magnetic)–probably just as tiny particles, not large enough to really be noticable, but just enough for the rock to be attracted to a very strong magnet; this is very common for such a rock. A rock like this is probably not magnetic enough to be attracted by an “old style” common bar magnet, but enough to attract one of the modern, high strength rare-earth-based “supermagnets”…
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