Fig. 2: Photographs of a fragment of the articular cartilage of STM4-3 seen with multiple microscopy methods.

a Femur fragment (ff) seen under transmitted light. b Fragment seen under the polarized light. c Close-up of the fragment (green box in a) showing dark tissues and overlying sediment. d Close-up of the fragment (pink box in b) seen under overexposed polarized light, showing sediments (sed), calcified cartilage (cc), and a few subchondral bone trabeculae (bt) that are birefringent. The two tissues are infiltrated with an orange to dark red material mostly composed of iron (Fe). e A close-up on the cartilage reveals that a lot of the chondrocyte lacunae are filled with the orange iron material. f Close-up of the white box in e, with arrows pointing at a few chondrocyte lacunae. g SEM image of approximately the same area shown in e, showing calcified cartilage with chondrocyte lacunae filled with 2 types of material: a dark gray material and a lighter material. h–k EDS analysis on this same image (g) showing the calcium (Ca) of the extracellular matrix, a group of chondrocyte lacunae filled with Silicon (Si) and Aluminum (Al), and another group with lacunae that are filled with iron (Fe). l Close-up of the white box in (g) showing ironized cartilage cells (icc) and silicified cartilage cells (scc).