|Ig. Home | Simp.Class. | Advanc.Class. | Alpha.List | Bowen's Reac.Srs. | ID Keys | Extrus/Intrus | Tect. | Self Tests|
The percent abundance chart helps to estimate how much of each mineral is present in a rock. Imagine each circle equals 100%; the black spots then equal the percent written under each circle. There are a few strategies that are helpful.
Begin with dark minerals; they are easier to see.
Begin with the least abundant minerals; they are easier to estimate.
Also, observe that a 50% abundance looks like a lot more than 50%. In this case dark minerals are easier for the eye to see and so we tend to overestimate them.
Finally, make sure all your estimates add up to 100% plus or minus.