Specifications:

2012 Royal Mint Piedfort Queen's Diamond Jubilee £5 Five Pound Silver Proof Coin

Issuing Country: United Kingdom

Metal: Solid .925 Sterling Silver

Weight: 56.56 Grams / Diameter: 38.61mm

Quality: Silver Proof Piedfort

Issue Limit: 3,250 Worldwide

Presentation: Original Royal Mint Box with it's Certificate of Authenticity

For 2012 to commemorate the Queen's Diamond Jubilee the Royal Mint released a very Limited Issue Piedfort £5 Five Pound Silver Proof Coin struck in solid .925 Sterling Silver. 
The reverse design depicts an early portrait of Queen Elizabeth II with foliage which is a specific reference to Queen Victoria the only other Monarch to achieve her Diamond Jubilee.
The obverse design depicts Queen Elizabeth II in the present wearing Garter Robes.
Both the reverse and obverse designs have been designed by Ian Rank Broadley FRBS.
Piedforts are coins which have been specially struck on thicker than normal blanks. As their name suggests they are closely associated with France, where from the twelfth century they were apparently issued by the Kings as presentation pieces. In Britain the practice of striking piedforts is later and less frequent, but medieval and Tudor examples are known.
These legal tender coins have been struck to proof quality using specially prepared dies and highly polished blanks.