10 Pesos Proof 1999 (Unifaz): Value of the 2 oz Silver Millennium Piece

If you inherited a large silver Mexican coin dated 1999 that only has a design on one side, you have a 10 Pesos Prueba Unifaz, part of Mexico's Millennium Collection. Its value starts with the silver: at 62.03 grams of .999 fine silver (about 2 troy ounces), it has a hard floor tied to the current spot price of silver, plus a collector premium on top. In 2026, that means the metal alone is worth roughly the price of 2 ounces of silver, and a certified proof example sells for more.

"Unifaz" is Spanish for one-sided (uniface). This piece was struck with a design on only one face, a proof-only presentation format, not a coin that ever went into your pocket. "Prueba" means proof: mirror-like fields and frosted, matte relief. That combination is what makes it a collector item rather than spending money.

What this coin actually is

This is a special proof issue from 1999, tied to Mexico's turn-of-the-millennium series (Colección Milenio, México durante el segundo milenio). It was never meant to circulate. Key specs, which you should verify against your own piece:

• Metal: .999 fine silver (99.9% pure)
• Weight: 62.03 grams (about 2 troy ounces)
• Diameter: 48 mm (large, roughly the size of a silver dollar and then some)
• Edge: plain (smooth)
• Finish: proof (mirror fields, frosted design)
• Format: uniface (design on one side only)

The weight and diameter are your first authentication check. If your piece does not hit 62.03 grams and 48 mm, something is wrong.

What it's worth

Two things drive the price: the silver content and the collector premium for a proof, uniface piece in good condition. Because the metal is fixed at about 2 ounces of pure silver, this coin can never be worth less than melt value. What sits above that floor depends on condition and whether it's certified.

Condition	What it means	Typical value (USD)
Damaged / cleaned	Scratches, spots, wiped surfaces	Close to melt (about 2 oz silver spot)
Uncertified proof	Original look, no third-party grade	Melt plus a modest premium
Certified proof (NGC/PCGS)	Graded, authenticated, high PF number	Highest tier, premium over melt

We do not publish a fake exact figure for this issue because it trades thinly and the silver spot moves daily. Honest expectation: from roughly the value of 2 ounces of silver at the low end, up to a meaningful premium for a clean, certified proof. If you want a number for insurance or a sale, get it graded or appraised against the current spot price.

The official mintage for this issue is not published by Banco de México. When a mint does not release a figure, it usually means the piece came out in a restricted numismatic set or a very limited run. Collectors speculate on numbers online, but none are confirmed. Treat unverified mintage claims from sellers as marketing.

How to tell if yours is genuine

Silver at this size and value attracts fakes, so run these checks before you buy or sell:

1. Weigh it. It should read 62.03 grams on a kitchen or jewelry scale. Off by more than a fraction of a gram is a red flag.
2. Measure it. 48 mm across. Too small or too thick and it's not right.
3. The ping test. Real .999 silver rings with a high, sustained tone when tapped lightly. Base-metal fakes sound flat and short.
4. Look at the finish. A genuine proof has true mirror fields and crisply frosted relief. Fakes often look hazy or grainy.
5. Get it certified. For a piece worth real money, NGC or PCGS grading is the only definitive answer. It authenticates and grades in one step, and it raises resale value.

Use our coin grading guide to judge condition yourself before you spend money on certification.

Errors and varieties

Since this was struck in a single year (1999), there are no date varieties. There can be minor die varieties (letter positions, small striking anomalies) that only NGC or PCGS graders distinguish. Genuine mint errors (off-center strikes, die rotation, double strikes) can raise value sharply, but most "errors" posted online are post-mint damage: bumps, scratches, corrosion, not factory errors. If you think you have a real one, post clear photos in the Pesoteca forum and let the community weigh in.

Where to sell it

Because this is a precious-metal proof, sell only where you can show the buyer the actual coin and its weight, and where the buyer can verify before paying.

• Verified coin dealers: the Pesoteca dealer directory lists shops that appraise on the spot and pay against real spot pricing.
• Collector-to-collector: the Pesoteca buy/sell forum reaches people who understand what a uniface proof is and pay for it.
• Before you list: photograph the obverse, reverse (blank on a true uniface, so document that too), and the edge. Confirm the weight. Do not dump it to the first bidder on a general marketplace, where fakes are most common.

If your piece is clean and possibly high grade, certifying it first almost always nets a higher, faster sale.

Have a large 1999 silver Mexican coin and not sure if it's the real uniface proof or a copy? Post the weight and edge photos in the Pesoteca forum and we'll help you pin down what you've got.