Tiberium is like radiation sickness, at least that is how I see it. Around it long enough and the sim gets sick; has the green face and then the dash to the toilet. I've forgotten at least twice to remove it from my inventory after a trip. Have a sick sim and then remembered to check and yep, I had forgotten to put the tiberium outside.
I think, but not sure, that Carl mentions it in the guide, I think in the gem area.
If you have the gem cutter (can use the one at the elixer store if not) and place the dust on the ground and it will grow more tiberium. Once had four piles of tiberium and they all grew. Checked later and I have the first one and four others; all around $39,000 each.
Had placed the dust, it snowed and I forgot about them; then there are these weird green sparks coming out of the snow and I remembered I had tiberium dust.