A pearl is a hard organogenic object produced within the soft tissue of mollusc shells. Although these may also be legitimately referred to as pearls by gemological labs - "elephant pearls", "bamboo pearls" and a number of others. The Russian name "pearl" comes from the Chinese name "zhen zhu" ("珍珠") through Turkic borrowing.

Pearl used in the jewelry manufacture has many varieties and differs in appearance, spread area and the biological variety of its producing mollusks.
Types of Pearls and their largest producers ➝

Chemical composition: Aragonite (CaCO3 – rhombic crystal structure) is composed of a combination of albuminous compounds (conchiolin - common chemical formula C32H48N2O11); internal parts of natural pearls sometimes are composed of a calcite composition.

Color: Nacreous pearls occur in a range of a white and "cream" color. Rarer gems having the basic pink, green, blue, lavender or gold colors, as well as the gray and black. The pearl primary color is defined by organic material in the mollusc habitat, and the characteristics of the irritants in the pearls composition (that generally depends on the biological characteristics of mollusc). Besides the basic color pearls there are additional colors (overtone), caused by the effect of light refraction at the boundary layers of nacre. Some colors are referred to as "orient" that is nacreous play of additional colors.

Typical commercial colors of non-nacreous pearls are white, pink (to red-purple), yellow, orange, purple and violet, as there are colors, commonly widespread, but colors that are relevant to the jewelry are gray, brown to black, and colors with dirty shades of gray and brown tones. The color of non-nacreous pearls due to the color of albuminous compounds that are part of the shell (and participating in the pearls cultivation), and irritants the mollusc habitat.

Identification properties

Physical properties
Mohs hardness: 2.5-5
Density: 2.60 – 2.85 g/cm3
Cleavage: none
Fracture: uneven
Optical properties
Optical character: microcrystalline matter*
Refractive Index: 1.52 – 1.69
Birefringence: 0.156
Pleochroism: none
Dispertion: none
Luster: mother-of-pearl

* Sometimes anomalously biaxial (which refers to twins, and distorted crystals).

Inclusions and structural inhomogeneities


Inclusions and structural inhomogeneities


Inclusions and structural inhomogeneities