Short answer. It is a barter, not a loan. Under Article 1954, a contract in which one person transfers ownership of non-fungible things — specific, individually identified items — to another, in exchange for things of the same kind, quantity, and quality, is classified as a barter. The non-fungible nature of what was given is what determines the classification.
What the law says
A contract whereby one person transfers the ownership of non-fungible things to another with the obligation on the part of the latter to give things of the same kind, quantity, and quality shall be considered a barter.
Civil Code, Article 1954 — Non-Fungibles for Fungibles Is Barter. Read the full provision →
The distinction between barter and loan
A simple loan — or mutuum — involves the transfer of fungible things, with the borrower obligated to return the same kind, quantity, and quality. Fungible things are interchangeable: one unit is equivalent to any other unit of the same type (rice, money, generic metal ingots). A barter involves exchanging goods for other goods, often of different kinds. Article 1954 addresses the edge case: when the item transferred is non-fungible — specific, individually identified, irreplaceable — but the other party's return obligation is framed in terms of kind, quantity, and quality, the law classifies it as barter.
Why the piece of jewellery makes it barter
The piece of jewellery in your scenario is a non-fungible thing: it has individual identity — a particular design, craftsmanship, and history that distinguishes it from other pieces. You transferred ownership of that specific, unique object to the other person. The other person's obligation to return ten grams of gold of the same kind is framed in generic terms, but Article 1954 focuses on what was given, not what is to be returned. Because you gave a non-fungible, the transaction is barter under the law.
Practical consequences of the classification
The classification matters because the rules governing barter and the rules governing loans differ in important ways. A simple loan is governed by the provisions on the contract of loan — including rules on interest, on the obligation of a money borrower, and on the consequences when the same kind of thing cannot be returned. Barter is governed by a different set of provisions, with its own rules on warranties, rescission, and the obligations of both parties. Misclassifying the transaction can lead to applying the wrong legal standards when a dispute arises.
When the classification is less clear
Not every exchange involving non-fungible and fungible goods is an obvious barter. If the non-fungible item transferred had a monetary value that the parties explicitly agreed would be repaid in money — not in kind — that starts to look more like a sale or pledge than a barter. Article 1954 applies when the return obligation is framed as things of the same kind, quantity, and quality as the original, which is the typical barter structure. If your agreement calls for a specific peso amount rather than a quantity of gold, the contract may fall under a different category entirely.