Here is a view of the upper housing of a high volume pump. Note the scoring on the sides.

Those score marks are from debris that was sucked up into the pump. The foreign material was forced between the edge of the gear tooth and then dragged and ground into the machined surface. The stock Volvo oil pump housings are made from aluminum alloy. Most aftermarket pumps are also alloy housed. The Melling 181 replacement pump has an iron/steel housing.

The advantage of the aluminum housing, besides a weight savings, is that the foreign material would merely gouge the housing surface; and not cause the gear to bind and freeze up.

This view is of the inlet side.

[and no, I would not reuse this pump.]