Geochemistry

Analysis of Oxide Abundance

The eight most abundant elements in the Earth's crust are almost entirely found as oxides. Their typical abundance (by mass percent of the oxide form) is:

Silicon dioxide ( ):

Aluminum oxide ( ):

Iron(III) oxide ( ) / Iron(II) oxide ( ): combined

Magnesium oxide ( ):

Calcium oxide ( ):

Sodium oxide ( ):

Potassium oxide ( ):

Titanium dioxide ( ):

Conclusion

The most abundant oxide is (Option B).

The second-most abundant oxide is (Aluminum oxide).

This corresponds to Option (A).

Step 1: Understanding the composition of forsterite.
Forsterite has the formula . When it melts, it will produce a melt primarily consisting of magnesium oxide ( ) and silicon dioxide ( ).

Step 2: Calculate the molecular weights.
- Molecular weight of forsterite :

Step 3: Calculate the weight % of MgO in the melt.
The weight of MgO in the melt will be contributed by the magnesium part of forsterite, which is 2 atoms of magnesium (80.60 g/mol from ). The weight % of MgO in the melt is:

Step 4: Conclusion.
The weight % of MgO in the melt is 57.3%.

Step 1: Understand the molar ratio.
The molar ratio is given as 11. This means: We are given that the content in the rock is 0.62 wt%. Our goal is to calculate the weight percent of .

Step 2: Use the molar ratio to calculate the weight percent of .
First, we need to convert the weight percent of to moles, then use the molar ratio to find the moles of . 1. Moles of in 0.62 wt%: The mass of is 0.62 g per 100 g of rock. The moles of is: 2. Moles of : From the molar ratio , the moles of is: 3. Convert moles of to weight percent: The mass of is:

Thus, the weight percent of in 100 g of rock is:

Step 3: Conclusion.
The weight percent of is 10.4 wt%.