21. Which gemstone is known for its black color and is often used as a protective stone?
a) Obsidian
b) Onyx
c) Hematite
d) Jet
22. Which precious metal is commonly used for making engagement rings and wedding bands?
a) Silver
b) Platinum
c) Copper
d) Titanium
23. Which organization is responsible for grading and certifying diamonds based on the 4Cs (Cut, Color, Clarity, and Carat Weight)?
a) GIA (Gemological Institute of America)
b) BIS (Bureau of Indian Standards)
c) IGI (International Gemological Institute)
d) HRD Antwerp
24. Which gemstone is known for its blue-green color and is associated with December?
a) Emerald
b) Sapphire
c) Opal
d) Turquoise
25. Which term refers to a gemstone that has been cut and shaped with many facets to enhance its brilliance?
a) Cabochon
b) Faceted
c) Tumbled
d) Rough
