Healthy human bone tissue is naturally white or yellowish-white, composed of organic proteins and inorganic mineral compounds. A noticeable green hue indicates a chemical interaction has occurred, usually after death. This discoloration results from the bone’s porous structure absorbing foreign elements or byproducts from its immediate environment. The green color can be traced to a few distinct mechanisms, including biological breakdown processes and the absorption of metallic compounds.
The Chemical Process of Post-Mortem Discoloration
The most frequent cause of a green tint on skeletal remains is the body’s natural breakdown after death. This process, known as putrefaction, involves gut bacteria consuming soft tissues and producing various gases as metabolic byproducts.
A key chemical produced during decomposition is hydrogen sulfide gas (H2S). As red blood cells break down, the iron-containing protein hemoglobin is released into the surrounding tissues. The hydrogen sulfide reacts chemically with the iron atoms released from the hemoglobin, forming iron sulfide, a dark, inorganic salt. Iron sulfide creates a green-black discoloration that first appears in soft tissues, but can eventually stain the surface of the bone.
External Environmental Staining
When bone is exposed to certain environmental elements, it can absorb external chemicals that cause a surface stain. The most common source of this green discoloration is the presence of copper or copper alloys near the remains. Items like copper jewelry, coins, or buttons can leach metallic salts into the surrounding soil. Over time, these copper salts—such as copper carbonate (malachite)—dissolve and are absorbed into the porous mineral structure of the bone.
The copper ions react with the calcium phosphate in the bone matrix, creating a stable, bright greenish-blue stain. This process is frequently observed in archaeological contexts when remains are found in close contact with copper artifacts. The resulting color is more vivid and localized than decomposition staining, often appearing only where the bone touched the metal object or was submerged in copper-rich soil.
Rare Physiological Pigment Accumulation
In very rare circumstances, a green color can be caused by the accumulation of biliverdin, a natural internal pigment. Biliverdin is a green bile pigment produced during the normal breakdown of red blood cells, which is usually quickly converted to bilirubin and excreted.
However, severe liver disease or profound jaundice can overwhelm the body’s ability to process these pigments, leading to high concentrations in the bloodstream. The green biliverdin can then saturate and deposit into calcified tissues, potentially causing a greenish tint in the underlying bone matrix. This phenomenon is clearly illustrated in certain animals, such as the garfish, whose bones are naturally green due to high biliverdin concentration. In humans, a visible green coloration from this internal physiological cause remains a highly uncommon finding.