Most common salivary gland involved by stone is

Eighty percent of all salivary stones occur in the submandibular gland, 10% occur in parotid, 7% in the sublingual and the remainder occurs in minor salivary glands" Eighty percent of submandibular stones are radio-opaque and can be identified on plain radiographs. In contrast parotid stones are usually radiolucent and rarely visible on plain radiography. Ref : Bailey & Love 25/e p755