Gem collecting

Gems are collectibles in The Sims 3.

Raw
Gemstones are found in the rough.

Tiberium
Tiberium, an easter egg referring to the Command & Conquer series, is an extraordinarily rare and potentially very valuable. The raw rock is worth around §100. In inventory (either as ore or cut) it will give a negative moodlet. For §6500 you can get the gem spire-cut, which will in one day grow into a Large Spire (either in inventory or on the ground) which will sell for over §40,000 each, and if left outside may even spawn more Tiberium spires. Alternatively you can get the heart-shape cut which will also grow. Selling a heart-shape cut or a small spire cut will roughly break even with the cost of cutting.

The easiest way to get Tiberium is to break space rocks with the board breaker (requires Level 9 Martial Arts) - having completed the Athletic Strength challenge is immensely helpful as you won't get fatigued. Sometimes relic vendors have them, notably in Egypt.

Tiberium in all forms glows green and will make a soft "ping" sound if placed on a lot.

Note: I have had a different experience. I found Tiberium in the Masoleum and placed it on my lot, as I did not have the required cut yet and it was making my sim ill. It grew into a 'Large Spire Cut Tiberium' after a few nights, without being cut at all. It is worth $40434.

Cuts
Gems may be sent to the gem-cutter and cut into the following cuts. You start with the Emerald cut, and gain cuts by cutting gems.

Geode & Septarian Nodules only have Polished Split and Heart-Shaped cut, while Tiberiums only have Spire and Heart-Shaped cut

Sometimes the gemcutters will return an uncut gem, saying that it is actually a Mysterious Mr. Gnome in disguise.

The table lists both when you break even with a particular cut, and when a cut begins yielding better profit than the previous cut.

For example, if a gem is worth §47, an oval cut provides §70 while the Pear cut yields §82. Factoring in the cost of the gem and the cost of cutting the gem, the Oval cut provides a §3 profit while the Pear cut yields no profit. The Pear cut does not start providing more profit than the Oval cut until the original worth is §60, as listed below.