According to Bowen's Reaction Series with decreasing temperature

• A. Quartz is first
• B. Olivine is first
• C. Muscovite is first
• D. K-feldspar is first

Answer: (B)

As magma cools, minerals crystallize in a specific order, with the highest-temperature stable minerals forming first. Olivine is stable at the highest temperatures among common rock-forming minerals, so it crystallizes early as the melt begins to cool. As olivine is removed from the melt, the remaining liquid evolves toward compositions that favor minerals that crystallize at lower temperatures. Quartz, potassium feldspar, and muscovite require further cooling and higher silica contents, so they appear later in the sequence. Therefore, olivine is the first mineral to crystallize as temperature decreases.