I gave a pearl necklace for my sister's birthday.

Literal

Younger-sister [possessive-の] birthday [on-に] pearl [possessive-の] necklace [object-を] presented.

贈る (おくる, 'to present/gift') is more formal than あげる — it implies a deliberate, perhaps ceremonial gift. 真珠 (しんじゅ, 'pearl') is a Sino-Japanese compound.