Compare the ways in which ironmagnesium minerals and feldspars crystallize from magma?

Answer 1

In Bowen's reaction series, feldspar minerals go through a continuous change of composition, while iron-magnesium groups have an abrupt change of mineral types.

When magma cools, the feldspars that form are calcium-rich. As cooling continues, the feldspars react with magma and the feldspar composition changes. The result is a zoned crystal with sodium-rich outer layers and calcium-rich core.

For iron-magnesium minerals, when magma starts cooling, a mineral begins to crystallize. However, when the magma temperature drops, a whole new mineral begins to form. The previously formed minerals reacts with the magma and is converted into the new mineral.

Answer 2

Iron-magnesium minerals typically crystallize earlier in the cooling process of magma compared to feldspars, as they have higher melting points. Iron-magnesium minerals are commonly found in mafic or ultramafic rocks, whereas feldspars are more common in felsic rocks. Additionally, feldspars are part of the silicate mineral group, whereas iron-magnesium minerals belong to the ferromagnesian silicates.