This mineral is the birthstone for the month of November; it is a silicate mineral of aluminum and fluorine and has Mohs hardness of 8. Name it.

This mineral is the birthstone for the month of November; it is a silicate mineral of aluminum and fluorine and has Mohs hardness of 8. Name it.

• A. Quartz
• B. Topaz
• C. Garnet
• D. Spinel

Answer: (B)

Identifying minerals by their chemistry and physical properties helps pin down the answer. This clue points to a mineral that is the November birthstone, is a silicate containing aluminum and fluorine, and has a Mohs hardness of 8. That combination describes topaz: it is an aluminum silicate fluorine mineral with the formula Al2SiO4(F,OH)2, and its hardness is 8 on the Mohs scale. Quartz is a silicate of silicon and oxygen but lacks aluminum and fluorine and is softer (hardness 7). Garnet is another silicate but has a different chemistry and doesn’t include fluorine. Spinel is an oxide mineral, not a silicate, and also doesn’t fit the fluorine-containing aluminum silicate profile. So topaz matches all the given clues.

Identifying minerals by their chemistry and physical properties helps pin down the answer. This clue points to a mineral that is the November birthstone, is a silicate containing aluminum and fluorine, and has a Mohs hardness of 8. That combination describes topaz: it is an aluminum silicate fluorine mineral with the formula Al2SiO4(F,OH)2, and its hardness is 8 on the Mohs scale. Quartz is a silicate of silicon and oxygen but lacks aluminum and fluorine and is softer (hardness 7). Garnet is another silicate but has a different chemistry and doesn’t include fluorine. Spinel is an oxide mineral, not a silicate, and also doesn’t fit the fluorine-containing aluminum silicate profile. So topaz matches all the given clues.