I think I've found a contradiction regarding the children of Abraham and Keturah.

Gen 25:1-2

1: Then again Abraham took a wife, and her name was Keturah.
2: And she bare him Zimran, and Jokshan, and Medan, and Midian , and Ishbak, and Shuah.

but Gen 25:4 says

And the sons of Midian; Ephah, and Epher, and Hanoch, and Abidah, and Eldaah. All these were the children of Keturah.

The first verse implies that Ephah, Epher, Hanoch, Abidah and Eldaah are all grandchildren of Keturah, but the fourth verse says that they are her children. I know that the christian response will be:

A) in verse 4, children=decendants

B) Midian's wife was also named Keturah

or the least likely:

C) Midian and his mother are the parents of the these children

While it's possible that either of these explanations reconciles any contradiction, I don't think that any of these are valid without any extra information.

KPB