Photomicrographs of siderite cements. (A) Natural transmitted light photomicrograph of a cemented fracture, barite (Brt) and posterior siderite (Sd3), containing no oil. Siderite crystal almost entirely plugs the fracture, except on the left bottom part of the image (Sample C2335, Roemerberg). (B) Transmitted polarised light photomicrograph of (A) (Sample C2335, Roemerberg). (C) Transmitted light photomicrograph of oil containing partially cemented fracture (Sd 2) (Sample E2674, Roemerberg). (D) Transmitted polarised light photomicrograph of (C) (Sample E2674, Roemerberg). (E) Transmitted light photomicrograph showing matrix siderite cement (Sd 1), and oil infill (Sample B-2680, Roemerberg). (F) Transmitted polarised light photomicrograph of (E) (Sample B-2680, Roemerberg).