A purple 3-bead necklace with an 18-inch adjustable chain would typically feature three distinct beads as focal points. The beads could be made of materials like glass, gemstones, or acrylic, with a rich purple hue ranging from deep royal purple to lighter lavender tones. These beads are likely spaced evenly along the necklace and may be smooth, faceted, or have unique textures for added visual interest.

The 18-inch adjustable chain allows for flexibility in length, so the necklace can be worn as a choker or slightly longer. The chain itself might be made of metal, such as silver, gold, or stainless steel, and includes an extender clasp or additional links for easy adjustment. The overall design would be elegant and versatile, perfect for both casual wear and more formal occasions.