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

Here's why:

* Peridotite is an ultramafic igneous rock, meaning it is very rich in magnesium and iron. It is primarily composed of olivine and pyroxene, with olivine being the dominant mineral.

* Gabbro is a mafic igneous rock, also containing pyroxene, but with a higher proportion of plagioclase feldspar.

While both rocks contain olivine, the proportion is significantly higher in peridotite.