It has a mean weight of 8.36 grams which very slightly more than the old Rs 2 coin. With a diameter of 26.4 mm it is just one millimeter larger than the old Rs 1 coin. It has a thickness of 2.1mm which was selected to be in between the Rs2 coin which is 1.7mm and the Rs5 coin at 2.7mm. This is to allow good resolution at coin vending machines. A round Rs20/- token I got recently to use with a coffee machine has a diameter of 25.8 mm a thickness of 2.1 mm and a weight of 8.05grams and close to the new Rs10/- coin. The 11 sided coin is like the Canadian $ coin which almost the same size at 26.5 mm but thinner at 1.75mm and therefore much lighter at 7 grams. By selecting a large odd number of sides it has a constant diameter and if rolled on a flat surface the center of mass of the coin remains steady without wobbling up and down.
The justification of using Coins rather than currency notes is because coins last more than 10 times longer than currency notes which need to be withdrawn from circulation when they get badly worn out. However those like bus conductors who handle large amount of small currency by hand prefer currency notes since they are folded horizontally and wrapped around their fingers. I spent a few Rs10/- coins in the bus the day they were issued to the public. It was fun to use them since they were the first time the recipient had encountered them, and were accepted after a hard look at it.
In 1940, just 70 years ago, 10 Rupees was the value of a Gold Sovereign. The Sinhala term "Silima" for the British denomination Shilling was 50 cents. With a Gold sovereign now costing more than Rs 30,000/-, it is ironic that at the time the Rs10/- coin is being introduced it's buying power is less than the half cent coin when it was demonetized in 1941.
This being the case, one is surprised why CBSL continues to mint 25cent and 50cent coins which are very rarely seen in general circulation. Occasionally I have got two 50cent coins from a bus conductor who wants to get rid of them, most often he does not even bother to give Rs1 change, and does not fuss about getting Rs1 short.
The CBSL incurs a considerable loss minting these coins since it probably costs few times the face value to mint them. In theory it may be OK to release coins even if they costs more than the face value. This is on the poor assumption that they circulate freely. However when the face value drops below when it can be used to buy anything, any coins that one gets dropped into a till and goes quickly out of circulation. CBSL has a program to collect coins from tills in major religious sites to keep them in circulation, but has little access to tills at homes. Bus fare and item prices in shops no-longer use fractional rupee value. It is clearly time that CBSL made the Rupee the lowest legal denomination,
In many countries like Japan where the currency denomination is worth about a rupee the fractional denominations have been abandoned. USA is debating if to continue minting the one cent coin, and some European Union countries such as Finland and Netherlands produce them only for collector Mint sets. These are worth more than Rs1/-
CBSL has announced a new series of currency notes to be issued in 2010 August during its Diamond Jubilee celebrations. This series will not have a Rs10/- note. It is strongly rumoured that the new series will have a RS5000/- note instead of the Rs2000/- note which was first issued in 2006 October. I however hope CBSL will continue the new Rs2000/- notes since that denomination is needed. In USA the $20 cotes is the most frequently used note. The $50 and $100 is rarely seen in circulation.
Clearly the Rs5000/- is also needed, maybe even a Rs10,000/- since they now represent buying power less than the Rs500/- and Rs1000/- when the were first released in 1981. From over a 1000 years ago when when gold kahavanu were used, the highest denomination was usually about the value of an half sovereign now worth over RS15,000/-
The writer maintains an educational website on two thousand years of Lankan coins at coins.lakdiva.org, and is the new President of the Sri Lanka Numismatic Society.
An edited version of this article A new 10-rupee coin for your pocket By Kavan Ratnatunga appeared in the SundayTimes of Sri Lanka on 2010 April 11th
See also 2009 Sri Lanka - Ten Rupee in LakdivaCoins.