Apart from the year, the fact that Queen Elizabeth II has aged and a few commemorative coins with different designs, Australian decimal coins look pretty much the same as they always have. There are no longer any one or two cent coins and the One and Two Dollar coins have been introduced into the currency. See the Royal Australian Mint link below.
The Australian Twenty Dollar coin is not a general circulation coin and is minted for investors and collectors. The Twenty Dollar coin was only issued for the 1993 release of the "Centenary of the Modern Olympic Games" two coin set.
They are round, Proof in silver with 92.5% silver and 75% copper and weigh 33.62 grams.
They all have 20 DOLLARS clearly inscribed on them and the usual Queen Elizabeth II portrait on the obverse.
The reverse has one of two Olympic scenes depicting "Friendship" and "Fairplay".
The edge has the incuse inscription, "Citius, Altius, Fortius" (Faster, Higher, Stronger).
An Australian 1978 50 cent coin, like all other Australian 50 cent coins from 1969 to present, is made from a 75% copper and 25% nickel alloy and is 12 sided (dodecagonal). It weighs 15.5 grams and is 31.51mm in diameter.
The 1978 coin is a standard issue (non-commemorative) coin and features the Australian Coat of Arms on the reverse.
The obverse features the second portrait (by Arnold Machin) of a youngish, right facing Queen Elizabeth II with the words "ELIZABETH II Australia 1978" around the perimeter. The portrait of Queen Elizabeth II is the same for all Australian Coins issued from 1966 to 1984.
Pictures of a specific coin are difficult to come by.
The image at the link below shows the reverse design of the Australian Coat of Arms.
Such a coin does not exist. The last Australian 1 cent coins were issued for circulation in 1990. They were progressively withdrawn from circulation in 1992.
Other than the 1966 coin, the only round 50 cent coin ever issued, the Australian 50 cent coin is a cupro/nickel dodecagonal (12 sided) coin of silvery appearance and is often used as a commemorative.See the link below.
In Australia, the slang word for a 5-cent coin is a "zac" or "zack". Either way it is pronounced the same (like zak). The word, like the coin itself, is less common these days.
Apart from the 1966 round 50 cent coin, all Australian 50 cent coins are pretty much the same. The are 12 sided (or dodecagonal) and are made made from 75% copper and 25% nickel giving them a silvery appearance. The edge is plain, they are 31.51mm in diameter and weigh 15.55 grams. All Australian coins have the reigning Monarch on the obverse, currently Queen Elizabeth II, and the Australian Coat of Arms featuring a kangaroo and emu on the reverse. The Australian 50 cent coin is often used as a commemorative coin and the reverse will have a different design. See the link below.
If by a "mule" coin you mean for example, a 1999 Australian 2 Dollar coin reverse struck with the obverse of a different coin, like a similar size New Zealand coin or, on an Australian 10 cent blank, this is an accident of the minting process and a valuation cannot be anticipated. Examples of your coin have sold on eBay for up to $26 AUD. A reputable coin dealer will be able to give a more accurate valuation based on inspection of your coin.
All Australian silver coins (5, 10, 20 and 50 cent) are composed of 75% copper and 25% nickel. The standard issue Australian 20 cent coin has Queen Elizabeth II on the obverse and a platypus on the reverse with a "20". They have a milled edge, weigh 11.31 grams and are 28.52 mm in diameter. The Australian 20 cent coin is occasionally used as a commemorative and the reverse design will be different from the usual. See the link below.
Neither Australia nor New Zealand has ever produced a 45 cent coin.This is mostly because a 45 cent coin would be highly impractical, it isn't a round denomination like a 20 or a 5 cent coin. It also doesn't fit into a dollar like a 25 cent (american quarter) does.
Ascent (a cent).
its a big huge coin that is silver. its basically a fifty cent worth .
A US one cent coin dated 1906 is a Indian Head (1859-1909) cent.
Hmm... "Liberty one cent"? Im not sure if there is a coin like that.MoreALL American coins have the word LIBERTY or a picture of Miss Liberty on them. Your coin, like all other cents minted since mid-1909, is called a Lincoln cent. There's more information at the Related Question.
About the width of a US penny (one cent coin)