Below are some more hematite concretions from the country of Georgia. Thanks to Besik for the photos.

Here are some from China. Thanks to Julia for the photos.

Here are some more from the U.S. Thanks to Cary for the photos.

Here are good ones from Isabelle, who found hers in Australia (left), and Jean, who found hers in Massachusetts (right).

Thanks to Micah, here are two views of another one from Missouri.

Thanks to Theresa for two views of a concretion from Texas.

I found two envelopes in my mailbox one day. One, from Texas, had the stones on the left. The other, from Wyoming, contained the stone on the right. All are hematite concretions. Thanks Frank and Joe.

Thanks to Warwick from Australia for these two.

Thanks to Ben for these two views of a hematite concretion

A most excellent specimen of what I call a dog-turd concretion. Thanks to Mason in Texas.

Thanks to Ron from Missouri for these two holey hematite concretions.

Thanks to Christine for this one.

Thanks to Adam for this fine specimen.

Thanks to Toby for this one from the Sahara.
    

This one's from Steve in Portland.

Thanks to Mark for this one.
  

Here's a likely candidate, from Peru! It resembles meteorwrong no. 194. Thanks Jon.

  
Sometimes hematite makes coatings on other rocks. Thanks to Scott for this one.

Here are two other examples hematite coatings. Thanks Tom and Søren.

Here are two other examples hematite coatings. Thanks Tom and Søren.

  
I was given the stones below as a child by my grandmother. I don't know where she got them, but she was from New York state. She called them "Indian paint pots." (See, for example, Garvies Point concretions). The stones are hematite concretions used by native Americans to paint their faces. The blunt end of the stone in the upper left could be rubbed in the bowl of another stone with water (we used saliva as kids, of course). A reddish paste was produced because hematite concretions are not particularly hard (which is why they make a red streak in the streak test, below). Because of their high density, large hematite concretions have been used since prehistoric times for tools (see Lithic Casting Lab).