Coin 1925 year of release

This year, the newly-formed USSR printed penny coins of various denominations, starting with a silver fifty kopeks (50 kopecks) and ending with a copper coin worth half a penny.
The weights of the coins were borrowed from the royal designs, and this was due to the technical features of the equipment on which they were minted.
Until July 1925 half a penny, 1 and 2 kopecks were minted from copper. Since July, they used aluminum alloy (10%) and copper (90%), as a result of which the coins became lighter and their color became golden.
Trial lots of coins of 10 and 20 kopecks from bronze were also minted, now they are very rare, as well as copper 1 and 2 kopecks.
So, now coin collectors collect such coins:
- 50 kopecks (fifty kopecks), material - silver samples 900, weighing 9-10 grams and a diameter of 26.67 millimeters, 3 modifications were issued, the most rare and expensive - with a smooth herd;
- 20 kopecks, material - silver samples 500 and bronze, weighing 3.4 grams and 21.8 millimeters in diameter, 2 modifications were issued, one of them, where the letters of the USSR are rounded - very rare;
- 15 kopecks, the material - silver sample 500, weighing 2.5 grams and a diameter of 19.56 millimeters;
- 10 kopecks, the material - silver sample 500, weighing 1.8 grams and a diameter of 17.27 millimeters;
- 2 kopecks, material - copper, weighing 6.55 grams and 24 millimeters in diameter, a coin very rare;
- 1 kopek, the material is copper, weighing 3.27 grams and 21.3 millimeters in diameter, was issued in two versions, the coin with the elongated letters of the USSR is very rare and expensive.
This year 1 copper coin weighing 4.4 grams and 22 millimeters in diameter was also released, a very rare and valuable coin from the trial lot.
Also in 1925, gold chervonets was released, but they did not take part in money circulation in the country. The circulation of the issue of this coin, and why it is so rare, is still unknown.