The mineral present in much greater quantities in peridotite than gabbro is olivine.

Here's why:

* Peridotite is an ultramafic rock, meaning it's very rich in magnesium and iron. It's primarily composed of olivine (Mg,Fe)2SiO4, with smaller amounts of pyroxene and other minerals.

* Gabbro is a mafic rock, meaning it has a higher content of magnesium and iron than felsic rocks but less than ultramafic rocks. Gabbro contains a mix of minerals like plagioclase feldspar, pyroxene, and olivine, but olivine is less abundant than in peridotite.

Therefore, peridotite has a significantly higher concentration of olivine compared to gabbro.