Every so often, a coin surfaces that seems to break the basic rules of minting. The 1970-S “Gold Washington Quarter” is one of those coins. At a glance, it looks like an ordinary Proof Washington Quarter from the San Francisco Mint. Flip it over and examine it closely, though, and the story changes entirely: buried beneath John Flanagan’s familiar Quarter design are the unmistakable remnants of an 1898 Liberty Head Half Eagle a $5 gold coin struck 72 years earlier.
This is not a coin plated in gold or dipped for effect. It is a genuine $5 gold piece that somehow found its way into a 1970 Proof coining press at the San Francisco Mint, where quarter dies came down on top of it, fusing two entirely different eras of American coinage onto a single planchet. Believed to be unique, the coin has already been featured on the cover of Mint Error News Magazine and graded by both NGC and PCGS. Now it is headed to public auction, with bidding through GreatCollections scheduled to close on September 13, 2026.
Specifications at a Glance
| Category | Detail |
|---|---|
| Country | United States |
| Date on Coin | 1970-S |
| Denomination Struck | Washington Quarter Dollar |
| Mint | San Francisco |
| Design Used | John Flanagan’s Washington Quarter |
| Host Coin | 1898 Liberty Head Half Eagle ($5 gold) |
| Host Coin Designer | Christian Gobrecht |
| Host Coin Composition | 90% gold, 10% copper |
| Error Coin Weight | 8.3 grams |
| Standard 1898 Half Eagle Weight | 8.36 grams |
| Standard 1898 Half Eagle Diameter | 21.65 mm |
| Standard 1970-S Proof Quarter Weight | 5.67 grams |
| Standard 1970-S Proof Quarter Composition | Copper-nickel clad outer layers over a pure copper core |
| Standard 1970-S Proof Quarter Diameter | 24.30 mm |
| 1970-S Proof Quarter Mintage | 2,632,810 |
| 1898 Philadelphia Half Eagle Mintage | 633,420 |
| Current Grade | PCGS Proof-66 |
| PCGS Certification Number | 48183803 |
| Prior Certification | NGC PF66 |
| Rarity | Listed by GreatCollections as “Believed Unique” |
| Auction House | GreatCollections |
| Auction Close | Sunday, September 13, 2026, at 7:07:05 p.m. Pacific Time |
The coin’s 8.3-gram weight is the clearest physical fingerprint of what happened here far closer to the 8.36-gram standard for an 1898 Half Eagle than to the 5.67 grams expected of a normal 1970-S Proof Quarter.
The Auction and Bidding Process
Because this coin is being sold through a live numismatic auction rather than an official Mint release, there is no fixed price, purchase limit, or ordering form involved instead, prospective buyers should understand the bidding mechanics:
- Platform: The auction is being conducted through GreatCollections, an established numismatic auction house.
- Closing date and time: Bidding is scheduled to close on Sunday, September 13, 2026, at 7:07:05 p.m. Pacific Time.
- Certification on file: The coin is currently encapsulated by PCGS as Proof-66 under certification number 48183803, with a prior NGC PF66 grade also part of its documented history bidders can independently verify both.
- Uniqueness claim: GreatCollections markets the coin as “Believed Unique,” meaning no second example has been confirmed to exist, which typically drives stronger competitive bidding on error coins of this caliber.
- Provenance to review: Interested bidders should review the coin’s full ownership and grading history, including its earlier NGC certification and its appearance in Mint Error News Magazine, before bidding.
- Typical auction house practices: As with most major coin auctions, expect a published lot description, high-resolution imagery, and a buyer’s premium added to the final hammer price bidders should confirm GreatCollections’ current terms before participating.
Given the coin’s singular nature, final price will likely be determined entirely by competitive bidding among advanced error-coin collectors rather than any pre-set valuation.
Historical Background
The Host Coin: 1898 Liberty Head Half Eagle
The $5 gold piece that unknowingly became the foundation for this error was originally struck as a Liberty Head Half Eagle, a design created by Christian Gobrecht that anchored much of America’s 19th-century gold coinage. The Philadelphia Mint produced 633,420 examples of the 1898 Half Eagle, coins that were fully struck, released, and presumably circulated or held in commerce for decades before this particular piece met an unusual second fate.
The Overstriking Coin: 1970-S Washington Quarter
The Washington Quarter design itself dates back to 1932, created by sculptor John Flanagan to commemorate the bicentennial of George Washington’s birth. By 1970, the design was a familiar fixture of American coinage, produced in enormous numbers for circulation as well as in smaller, more carefully controlled Proof format at the San Francisco Mint for collectors. The 1970-S Proof Quarter alone saw a mintage of 2,632,810 a routine production run that, in this one case, intersected with a 72-year-old gold coin already in existence.
How the Error Occurred
Proof coinage in 1970 was a hands-on process. Mint technicians fed individually prepared, highly polished planchets into specialized presses, and finished coins were inspected and packaged under tight quality control. Somewhere in that chain, an already-struck 1898 Half Eagle entered the Proof production line reserved for 1970-S quarters. Quarter dies then struck directly over the existing gold coin, overlaying Flanagan’s design atop Gobrecht’s decades-old Liberty Head Half Eagle. Exactly how the older gold coin entered that production stream at San Francisco has not been documented in surviving records only the physical coin itself remains as evidence of what took place.
A separate but relevant chapter involves a cache of several hundred U.S. error coins, including other Proof errors, that surfaced from a safe-deposit box in the early 2000s. That group was purchased by error specialist Fred Weinberg, reviewed by the United States Secret Service, and subsequently released to the California State Controller’s Office of Unclaimed Property, which auctioned the coins into the marketplace. That episode illustrates how significant Proof errors have historically made their way from Mint custody into private hands, though it should not be assumed to explain this specific coin’s path.
Description of the Obverse and Reverse
Obverse
At first glance, the obverse presents Flanagan’s familiar profile of George Washington, facing left, with “LIBERTY” arcing above his head and the date “1970” below. Because the underlying Half Eagle was already a fully struck coin before the quarter dies came down on it, portions of the original gold coin’s design can still be traced beneath the Washington portrait under close inspection, softened but not fully erased by the second strike.
Reverse
The reverse is where the coin’s extraordinary nature is most visible. Flanagan’s heraldic eagle, wings spread and perched above crossed olive branches, occupies the design space alongside “QUARTER DOLLAR” and “UNITED STATES OF AMERICA.” Remarkably, remnants of the original 1898 date from the underlying Half Eagle remain legible above the words “QUARTER DOLLAR,” a ghostly trace of the coin’s earlier identity peeking through its 1970 overstrike. Additional faint elements of the Liberty Head Half Eagle design survive on this side as well, giving collectors a rare opportunity to see two separate centuries of American coin design occupying the same small piece of gold.
Why This Matters for Collectors
- It may be a true one-of-one. GreatCollections lists the coin as “Believed Unique,” placing it in the rarest possible category of mint error — a coin with no confirmed twin.
- It bridges two centuries of coinage. Few errors allow a collector to see a 19th-century gold design and a 20th-century clad design occupying the same coin, struck 72 years apart.
- Gold overstrikes command outsized attention. Comparable errors such as a 1913 Buffalo Nickel struck on a $5 Indian Half Eagle planchet ($400,000) and a 1915 Panama-Pacific gold Half Dollar ($750,000) show that gold-related mint errors consistently draw premium prices relative to their base-metal counterparts.
- Its grade has held up remarkably well. Despite surviving over five decades and an unusual second strike, the coin still holds a Gem-level PCGS Proof-66 grade, with clean, well-preserved surfaces.
- Documented certification history reduces risk. The coin’s move from an NGC PF66 grade to its current PCGS Proof-66 holder, along with a specific PCGS certification number, gives bidders a verifiable paper trail uncommon for such an unusual piece.
Quick-Reference Buying Guide
- Confirm the auction details. Verify the current listing directly through GreatCollections and note the exact closing time September 13, 2026, at 7:07:05 p.m. Pacific Time.
- Review the certification. Check PCGS certification number 48183803 directly on PCGS’s verification system, and review the coin’s prior NGC PF66 history for consistency.
- Study high-resolution images before bidding. Look closely at the reverse for the visible remnants of the 1898 date and underlying Half Eagle design.
- Research comparable gold-overstrike errors. Review past results for coins like the 1913 gold-planchet Buffalo Nickel and 1915 Panama-Pacific gold Half Dollar to understand pricing context for major gold mint errors.
- Set a bidding limit in advance. Because the coin is believed unique, competitive bidding can escalate quickly decide on a maximum bid based on your own research rather than in the moment.
- Account for buyer’s premium and fees. Confirm GreatCollections’ current buyer’s premium and payment terms before your final bid.
- Arrange secure storage in advance. Given the coin’s rarity and value, plan for insured shipping and secure long-term storage before the auction concludes.
- Keep full documentation after purchase. Retain the auction record, certification details, and any provenance information provided, as this history will matter for future authentication or resale.
