When checking war assets, mineral resources gives 10, 25 or 100.
To receive 10 war assets
The minerals scanned in ME2 are lower than 100 000
To receive 25 war assets
The minerals scanned total over 100 000 each except element zero which can be below 100 000
To receive 100 war assets
In ME1
UNC: Prothean Data Discs. Need to collect 7
UNC: Turian Insignias. Need to collect 13
UNC: Valuable minerals. Heavy Metals need to collect 20
Rare Metals need to collect 20
Light Metals need to collect 20
Gasses need to collect 6
UNC: Locate signs of Battle. Salarian ID Tags need to collect 3
League of One Medallions need to collect 10
For ME2
Need 100 000 for each resource collected through planet scanning
When I did this, I started with 52 500 of each for importing a save from ME1, so I don't know if that counts towards the number. I collected over 100 000 for each just to make sure
Some helpful tips
When collecting the items in ME1, once you have the correct number, that item will not be highlighted anymore and turn gray indicating that number has been fulfilled. But there are more of that item in the game and if you collect another of that same item, it becomes highlighted again. Not sure if that will cause a problem when importing into ME3. The imported save might think that item still needs to be collected. As a suggestion, I would collect only the required number for that item
In ME2, I would collect the required resources needed before doing the suicide mission because you may decide to import your save right away into ME3 and if Mordin is killed during the suicide mission, the cost of upgrades increases with him not being there causing you to do more scanning then what is necessary.