Alizarin red is a dye derived from the anthraquinone family. It is commonly used in histology to highlight tissue calcium deposits by binding to calcium through a chelation process. This reaction allows the formation of red alizarin -Calcium complexes, a birefringent compound whose deposits appear in red under an optical microscope.

The reaction is not totally specific for calcium because other compounds can react with this dye such as magnesium, manganese, iron, barrium and strontium. But most of the time there is no interference since these compounds are not found in sufficient concentration in biological tissues to be able to interact with calcium staining.

Alizarin red stain is used to detect the presence of calcium deposits in a tissue or vascular system. It can also be used to characterize bone growth, osteoporosis or bone marrow in the study of cell signaling, gene expression, mesenchymal stem cells, ...