1978 Silver Onza Troy: Value & How to Sell It

If you inherited a heavy Mexican silver coin dated 1978 with no face value on it, you likely have an Onza Troy de Plata Pura, the coin that came before the famous Onza Libertad. Most sell in the range of 30 to 60 dollars, driven mainly by silver content and condition, not age.

What this coin actually is

The 1978 Onza Troy de Plata Pura (Spanish for "pure silver troy ounce") is a Mexican silver bullion coin struck by the Casa de Moneda de México, the Mexican Mint. Here is the part that trips people up: despite the name "plata pura" (pure silver), it is not .999 fine. It was struck in .925 sterling silver, the same fineness used in silver jewelry and flatware.

This coin carries no denomination in pesos. Its value is stated as the ounce itself, and the design guarantees the silver content. That is why you will not find a number like "1 peso" or "5 pesos" on it.

What is the 1978 Onza Troy worth?

This is a bullion coin, so it has a price floor tied to its silver content. At .925 fineness and 33.625 grams total weight, it contains roughly 31.1 grams (one troy ounce) of pure silver. That means its melt value tracks the daily spot price of silver, and it will never sell for less than that metal value.

For most examples in circulated or average condition, expect the melt value plus a small collector premium: commonly 30 to 60 dollars depending on the silver market. Coins that survived without scratches, cleaning, or handling wear are the ones collectors compete for, and those bring a stronger premium. A certified example in high mint-state grade can sell for more, but this is not a rare four-figure rarity. Anyone telling you a common 1978 Onza is worth thousands is wrong unless it is a verified error or a top-population certified grade.

Value here is set by two things: silver content (the floor) and condition (the premium). Age alone adds almost nothing.

Why collectors want it anyway

The 1978 Onza belongs to the first era of Mexican silver ounces, the direct ancestor of what later became the Onza Libertad that collectors know today. In these early years the coin was still struck in .925 sterling, not the .999 pure silver that came later. That makes it a bridge between the old sterling tradition and the start of Mexico's most famous modern silver series.

Because it is an early issue, it is harder to find in strong grade than recent Libertad coins, and its .925 fineness sets it apart at a glance from later strikes. It adds depth to any collection of Mexican silver ounces because it shows where the whole series began.

How to tell if yours is genuine

Start with a jewelry scale and a caliper. Compare against the specs above: 33.625 grams and 41 mm. Fakes usually miss on weight or diameter, show flat or mushy relief, or have off tone in the fields. Be suspicious of any offer priced well below the coin's silver value, that is a classic sign of a counterfeit or a scam.

For a coin worth this much, professional grading from NGC or PCGS is only worth the cost if you have a high-grade example, since certification fees can exceed the coin's premium on an average piece.

Where to sell it

Because this is a precious-metal coin, deal only with a buyer who will inspect the piece and its weight in front of you. Photograph the obverse, reverse, and edge before you talk price. Your safest options:

• A verified coin shop from the Pesoteca dealer directory, which can appraise it on the spot.
• The Pesoteca buy-and-sell forum, where collectors trade directly.

Avoid dumping it on Facebook to the first person who offers. Check the silver spot price the day you sell so you know your floor, and always review the grade and clear photos of both sides before agreeing to anything.

Got a 1978 Onza Troy in your inherited coins and not sure what grade it is? Post clear photos of the front and back on the Pesoteca forum and the community will help you pin down its value.

The Onza Troy de Plata Pura is the first official Mexican bullion series of the modern era. Originally struck in 1949 with a single mintage of 1,000,000 pieces, the series remained discontinued for nearly three decades until its resumption in 1978 with the denomination KM# M49b. Between 1978 and 1980 three annual issues were struck with minor varieties by year in the position of the scale and typographic spacing. In 1982 this series was discontinued when the .999 pure silver Onza Libertad began, formally authorized by decree of the DOF of July 14, 1982. The Onza Troy was struck in .925 silver (not in .999 like the later Libertad), with a gross weight of 33.625 g containing exactly 1 troy ounce (31.103 g) of pure silver. The nickname "Onza Balanza" or "Balance Scale Onza" in international markets comes from the main motif of the reverse: the traditional scale of commerce. Resumption of the Mexican bullion series after nearly 30 years. Mintage of 280,000. Type 2 variety with close spacing in "DE MONEDA".