Alopecia areata is a disease that attacks your hair follicles (the part of your skin that makes hair). In most cases, hair falls out in small, round patches about the size of a quarter. This causes only a few bare patches. Some people may lose more hair. In only a few people, the disease causes total loss of hair on the head or loss of all body hair.
Turquoise is a blue-green mineral, a copper aluminum phosphate, valued for its rarity and unique hue, and widely used as an ornamental stone. Popular in the 16th century to adorn places of worship in Turkey, it was eventually traded in Turkish bazaars and brought to Europe by merchants and travelers.
Turquoise identification is something that I think has to be learnt over time and exposure to the material. You really can't be taught how to identify turquoise by pictures or in words. You can get a start there though!