Expert: George Ardies - 10/27/2009

Question
I found a strange looking rock on a old rock wall in southern Quebec,along the U.S. border.It's a burnt black/brown color on the outside,and shows signs of rust on the inside.It's very heavy for it's size,and a magnet will stick to it. It doesn't set off a metal detector. I've been told that it is not a meteorite.The whole thing  is covered in weblike, light green lines, that really stand out against the dark background. It broke apart along these lines.I've washed it off, and the lines jump right out at you when it's wet.Why will a magnet work, and not a detector ? Will a detector work on a meteorite ? I've showed it to alot of people, most of them farmers who have been picking stones off their fields for a long time ,and they say that it is unique. What could it be ?

Answer
It sounds like it is Hematite, except for the light green lines. Hematite is magnetic and rusty brown when weathered. The reason the metal detector doesnt work is probably due to the minor amounts of iron in the sample. Another potential mineral is Limonite, which is similar to Hematite, but sometimes is lighter coloured. A picture would be great. If you could send one, I would be certain.
George