This is a 10 cent split planchet error. A split planchet error is a coin that either partially or completely splits down the side edge. This typically occurs during the manufacturing process when the alloy of a blank is poorly mixed and contains impurities.

When the metal for a blank is rolled, the impurities in the alloy prevent it from bonding correctly. This can cause the coin to become extremely weak where the layers do not bond correctly. The weak bond is a similar defect that causes the lamination peel error. These impurities in the alloy; in extreme cases, cover the entire area of a blank. In some cases this can cause the coin fall apart with the application of very little force.

A partial split planchet error occurs when only part of the coin splits or peels away, this is also known affectionately as a 'clamshell' error because of its similarity in appearance to a clamshell. These partial splits are much more prevalent than a complete split. Although, any split is much less common than the die crack or lamination peel error. Having both sides of a matching split planchet (of the same coin), is much more desirable and valuable to some collectors, compared to just having one half of a split. Pricewise a split planchet coin will generally command prices far above face value.

The split planchet error is much more commonly seen across the cupro-nickel Australian decimal coins. This error rarely presents on the copper 1 and 2 cent coins, or across the aluminium-bronze $1 or $2 coins. Pre-decimal split planchets are also extremely rare compared to their decimal successors. 

This 10 cent coin up for sale has no date on the obverse of the coin, making it extremely difficult to identify further information about production. With the Lyrebird design on the reverse, all we can assume is coin was minted somewhere after 1966. 

Release: Unknown
Mintage: Unknown