Obverse: identify the front

The obverse depicts a coin press surrounded by the mint name CASA DE MONEDA DE MEXICO, with the issue year. Dated references distinguish wide spacing between DE MONEDA for the 1978 Type I and close spacing for the 1978 Type II and the later types. Read the whole legend, numeral shape and spacing when comparing a specimen.

Reverse: identify the back

The reverse depicts a balance scale and identifies the fine-silver amount, alloy fineness and nominal gross mass. The 1949 type uses a 480-grain fine-silver legend. The later family uses a one-onza silver legend and .925/33.625-gram specifications. In 1979, the position of the left scale pan relative to the word UNA distinguishes two cataloged types.

History and purpose

The historical .925 group has four distinct annual years with a gap between 1949 and 1978. The 1978 return introduced two spacing types, followed by two scale-pan types in 1979 and the 1980 family. Dated reference records distinguish these historical bullion pieces from the Winged Victory Libertad series starting in 1982. A series heading spanning several decades does not imply continuous annual production.

How to identify this variant

Match the actual annual year, coin-press obverse, balance-scale reverse, .925 legend and nominal 33.625 g standard. Dated reference records give a 41 mm diameter; Numista describes 41.5 mm for the family. Record an individual coin’s measured diameter and complete design instead of selecting its purity by diameter alone. Keep patterns, plated copies, altered dates, gold onzas and modern silver Libertads separately identified.

Understanding its metal content

The nominal gross weight includes both silver and the other alloy metal. Each correctly attributed piece uses the dated reference of 1 fine silver troy ounce. Three pieces therefore total 3 reference fine silver troy ounces and 100.875 nominal gross grams. The 33.625 g gross mass does not mean that the whole coin is pure silver. Wear or damage can affect an individual measurement. A dollar melt estimate also needs a current market quote and remains separate from an offer or collector valuation.

Dates, varieties and composition changes

Actual annual years are 1949, 1978, 1979 and 1980. M49a is the 1949 type. M49b.1 is the 1978 wide-spacing type; M49b.2 is the 1978 close-spacing type. M49b.3 is the 1979 close-spacing type whose left scale pan points to U in UNA; M49b.4 instead points between U and N. M49b.5 supplies the 1980 and catalog-labeled 1980/70 rows. An overdate belongs to its visible issue year. Different catalogs can use different overdate descriptions, so retain the exact source attribution for a suspected variety.

Melt value versus collector value

Date, letter spacing, scale-pan alignment, overdate detail, surfaces, provenance and condition can influence collector interest independently of fine silver. Photograph the identifying details before combining pieces in a holding. The calculator does not determine rarity, grade or a variety premium. Preserve original surfaces and established certification or attribution; cleaning or polishing can affect collector interest.

Authenticity and condition

Clear photographs of both complete sides and the edge, plus measured mass and diameter, help identify a candidate type. Compare any unusual date or spacing with the appropriate dated reference. A photograph or national mint legend cannot independently authenticate a specimen or assay its silver. Plated, cast, altered or doubtful pieces require individual examination. Avoid inferring a proof finish from shine.

Selling this coin

Sort historical .925 Onza Troy pieces by actual dated type and keep modern .999 Libertads separate. Include full obverse, reverse and edge photographs when requesting a CashForCoins appraisal, with close views of spacing or suspected overdates. State the quantity and any existing certification. An offer can depend on authenticity, condition and collector demand alongside silver content; the reference calculation is educational.

Sources and calculation methodology

Dated reference M49a and M49b.1–M49b.5 references describe .925 silver, 33.625 g gross mass and 1 reference fine silver troy ounce. Dated diameter is 41 mm; Numista lists 41.5 mm for the series. The difference in catalog diameter descriptions is disclosed; no alternate physical weight or purity is inferred. Actual annual years are 1949, 1978, 1979 and 1980. Annual years and meaningful design varieties are taken from the individual dated references. The nominal fine-silver reference applies to a correctly attributed historical .925 specimen. The gross mass includes the alloy and is distinct from the fine-silver amount. Source precision and type identity are stated explicitly so different bullion standards can be compared.

Common questions

References

• NGC dated historical sterling Onza M49a — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• NGC dated historical sterling Onza M49b.1 — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• NGC dated historical sterling Onza M49b.3 — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• NGC dated historical sterling Onza M49b.4 — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• NGC dated historical sterling Onza M49b.5 — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• NGC dated historical sterling Onza M49b.2 — dated identity, fineness, gross mass, fine silver ounces, diameter, actual annual years and design/variety details Dates: actual annual rows of this named sterling Onza type. (checked 2026-10-12)
• Numista: 1949 sterling Onza type and legends — design legends and independently stated 41.5 mm series diameter; image credit is not reusable photo permission (checked 2026-10-12)
• Numista: 1978–1980 sterling Onza types — later reverse legends, design attribution and independently stated 41.5 mm diameter; main photo noncommercial license not used (checked 2026-10-12)
• Banco de México: 1949 historical Onza coin and paired photographs, inventory 15767 — Exact 1949 KM M49a specimen identity and genuinely photographed coin-press/balance-scale designs with visible 0.925/33.625 gram legends; measured specimen weight and diameter are not substituted for NGC nominal specifications. (checked 2026-10-12)

Issue-year references

• NGC dated historical sterling Onza M49a
• NGC dated historical sterling Onza M49b.1
• NGC dated historical sterling Onza M49b.3
• NGC dated historical sterling Onza M49b.4
• NGC dated historical sterling Onza M49b.5
• NGC dated historical sterling Onza M49b.2
• Numista: 1949 sterling Onza type and legends
• Numista: 1978–1980 sterling Onza types
• Banco de México: 1949 historical Onza coin and paired photographs, inventory 15767

Content maintained by CashForCoins. Last substantive record update: 2026-10-12. Report a specification or attribution issue through our contact page.

Related coins

Mexican Silver Libertad Half-Ounce — 1991–1995

Photo credits and rights on the linked coin profile.

Mexico • 99.9% silver; remaining alloy metals not independently verified

Issue years: 1991–1995

Fine silver: 0.499500 troy oz

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