explains that dark colored icebergs are formed by a higher density of bubble-free ice with a greater amount of rock detritus from the base of the parent glacier. Reddit
, explains that dark colored icebergs may be green, brown, black or a combination of the colors. The Reddit user explains:
These icebergs have usually rolled over, exposing basal ice, or have emerged from below water level. The various coloration are caused by differences in density, air-bubble content and impurities... dark layers indicate the presence of rock materials derived from the base of the parent glacier. Occasionally, rocks may be found on the original upper surface of the iceberg. As the iceberg melts, these materials precipitate into marine or lake sediments.
A rather technical explanation you might think. But the photo above tells the story of this unusual form of iceberg.