Bowen's Reaction Series describes the sequence in which different silicate minerals crystallize from a cooling magma. It consists of two branches: a discontinuous series of ferromagnesian minerals and a continuous series of plagioclase feldspars. Minerals that crystallize first do so at the highest temperatures.
Step 1: Understanding the Question:
The question asks to identify the first mineral to form in the discontinuous branch of Bowen's Reaction Series, which corresponds to the mineral that crystallizes at the highest temperature.
Step 2: Detailed Explanation:
The discontinuous series describes how, as magma cools, one mineral is formed, and then as the temperature drops further, it reacts with the remaining melt to form the next mineral in the sequence. The order from highest temperature to lowest temperature is:
\[
\text{Olivine} \rightarrow \text{Pyroxene} \rightarrow \text{Amphibole} \rightarrow \text{Biotite Mica}
\]
The other options, Muscovite and Quartz, crystallize at even lower temperatures, after Biotite.
Since Olivine is at the beginning of this sequence, it crystallizes at the highest temperature.
Step 3: Final Answer:
Therefore, Olivine is the first mineral to crystallize in the discontinuous series.