Scanning electron micrographs showing: a. A stacked cluster of rhombic siderite crystals, b. Siderite crystal clusters filling a lithophysal cavity, c. Spherical and hemispherical clusters of rhombic siderite crystals lining a fracture surface. d. Internal structure of broken spherical siderite crystal clusters, e. Flattened disc-shaped cluster of siderite crystals, f. Flattened disc-shaped cluster of siderite crystals .