The entrance to Newgrange does have dry stone walling similar to other monuments , but it is not of quartz and nor original either , iirc . Quartz tends to fracture conchoidally rather than along structural planes making it useless for walling and thus necessitating a steel reinforced concrete wall to support the present façade of relatively small quartz stones (interspersed with granite , and gabbro cobbles ), not slabs , as we would expect for walling .
When large amounts of quartz are found associated monuments it is often as a covering , rather than a wall ,and never a vertical wall .
“We found that the quart/granite layer was thickest and most extensive in the area outside the tomb entrance and at each side of it that it decreased gradually in amount and extent until it virtually disappeared atK21 in the west and K 81 in the east “ i.e. a clear emphasis on the entrance just as is found at other monuments with no suggestion of a wall , but that is not how it is represented in the modern façade which is a homogenous feature for a much greater extent .

The ground under the quartz at Newgrange had been cleared of vegetation “” a subsoil surface from which the turf and humus had been cut off “ O ‘Kelly p68 , suggesting that it might have been in preparation for the quartz as opposed to the quartz collapsing on to vegetation .
As for where we stand now Gabriel Cooney’s “The wall is likely to stand for far longer in the present than it did in the past , if it ever did “ strikes a couple of pieces of quartz together .