I found this awesome rock full of quartz but it is also half limestone.
To answer this you need to understand the nature of magma sources and whoever gave you the questions needs to be more technically accurate as the issue is silica content not quartz content. AND you need to understand what Bowen's Reaction Series tells us to expect within magmas. 1. mantle infilling at the mid oceanic ridge as an example. highly mafic mantle material such as Olivine-- low in silica( SiO2 or SiO3 or SiO4). Grain size is governed by cooling rates not content so this answer is fine-ground mass owing to rapid cooling. fine-grained low silica 2. partial melting suggest low temperature and as silica/quartz has the lowest temperature of the silicates in Bowen's reaction series this answer is quartz. partial melting also suggest lower heat content leading to faster cooling and produces a finegrained ground mass bubt instead of mafic lava it is felsic and in the category of ryolite basalt. High silica grainsize could be large pwing to prior crystallization See for example Orbicular Granite 3. quartz but because a differentiated magma has already lost the bulk of early crystallizing minerals of Bowen's series (the higher temperature of solidus ones) such that mainly quartz is left for the remix. this magma is said to be enriched in silica and is very viscous (thick) creating rather vicious volcanic eruptions. silica=viscous=vicious is the mnemonic Assimilation is incorporation of the country rock as it ascends and that is usually but not always higher in silica this situation also suggests substantial chilling leading to fine-grained mass. TO reiterate: grain size related to cooling rates.
