The item  is a handmade resin coaster with an irregular, wavy edge, featuring embedded iridescent flakes and glitter. These types of coasters are made using epoxy resin and various decorative inclusions like gold or silver flakes and pigments. 
Key Features
Material: High-quality epoxy resin that is durable and often food-safe.
Design: The coaster has a unique, irregular, or scalloped edge. The clear, translucent resin is filled with sparkling, multicolored, and iridescent flakes that reflect light.
Functionality: It is designed to protect surfaces from water marks, heat, and scratches from cups or glasses.
Maintenance: They are typically not dishwasher or microwave safe and should be hand-washed gently with a soft cloth.