Thank you for submitting your item for appraisal. This appears to be a so called Morgan Silver Dollar from 1921, minted in San Francisco ( mintmark "S" below the laurel wreath). Over 20 million identical coins were minted that year in San Francisco. The coin in your possession is only in good condition at best. Only coins in much better or even uncirculated condition are considered to be rare and expensive. An uncirculated silver dollar of that year might sell for over one thousand dollars. The estimate is based on similar items sold recently at auction ( silver value is low right now). There is no measurement for the sentimental value you might attach to it.