Left: Wyoming; Right: Texas
Technically, this one is may not a “concretion,” but it’s rich in hematite.
Two views of one from Pennsylvania
Nevada, two views This grape-cluster texture is known as “botryoidal.”
Madagascar, two views
A beautiful specimen from somewhere in the U.S.
Top and side of one from Connecticut
Utah (left) and Ontario (right)
Texas (left) and somewhere in Canada (right)
Colorado (left) and Oklahoma (right)
Two views of a stone from South Carolina. This one and several others here were found by hunters.
Mexico (left) Illinois (right)
Somewhere, botryoidal (left) and Lebanon (right)
Texas. This concretion appears to have started as a mass of pyrite crystals (iron sulfide, cubic) and is in the process of oxidizing to iron oxide.
This thing started out as a several pyrite crystals but is now largely oxidized to hematite.
This is a cluster of pyrite crystals beginning to oxidize to hematite.
This one is fascinating in that one side (bottom) has a texture like some other concretions shown here but the other side (top) has features that resemble meteorite regmaglypts.
West Virginia. This grape-cluster texture is known as “botryoidal.”
This photo was sent to me by a fellow who found it while gardening in his yard in Kauai, Hawaii. I asked a colleague who lives in Kauai whether or not hematite concretions were found there. He said that limonite concretions did occur. Limonite is a mixed iron oxide-hydroxide. It’s possible that some of the other concretions depicted here contain limonite.
This one was sent to me from Iowa. It makes a red streak and does not attract a magnet, but the specific gravity is only 4.1. Pure hematite has a specific gravity of 5.3, so this rock must contain some low-density mineral like quartz or a carbonate in addition to hematite.
I suspect that this one, from Delaware, also contains mineral phases other than hematite.
This one also looks like hematite cement holding sand grains together.
Two examples of “dog-turd” concretions