Erythrite is a secondary hydrated cobalt arsenate mineral, also known as "red cobalt" or "cobalt bloom," that is typically pink to crimson red. It forms from the oxidation of cobalt-nickel sulfide deposits and is often found in radiating crystal groups, encrustations, or earthy masses. While a valued collector's mineral and a minor ore of cobalt, its softness makes it unsuitable for use in jewelry or ornamentation. 

Characteristics and formation Chemical formula: (Co_{3 AsO_{4})_{2}cdot 8H_{2}O)Color:

Ranges from purplish-pink to crimson, though higher nickel content can cause it to fade to paler pinks or even turn gray.Crystalline structure: It forms a continuous series with annabergite, a nickel arsenate, where nickel replaces cobalt in the structure.

Formation: It is found in the oxidized zones of cobalt and nickel deposits, often associated with other cobalt minerals and sometimes natural silver.

Hardness: Its hardness is very low on the Mohs scale (1 to 2), making it soft and brittle. 

Uses and significance Collector's mineral: Its striking color and aesthetic crystal formations make it a popular mineral for collectors.

Indicator mineral: Its presence can help in the discovery of more significant cobalt, nickel, and silver ores.

Cobalt source: Erythrite is a minor source of cobalt, a metal essential for many modern technologies, including batteries, laptops, and magnets.