First, alkaline magma intruded into the overlying sediments, crystallized out and formed gabbro and diorite massifs, such as the Harzburg gabbro.
A little later, silica-rich granitic magma rose, some intruding into voids and gaps in the older rocks, but most being created by the melting of existing sediments.
Today's blockfields of Brocken granite, as well as other rocks in the Harz National Park, particularly in the Oder valley, are therefore at least 10,000 years old.
At the southeastern foot of the Brocken lies the spa resort of Schierke.
Somewhat to the north below the summit of the Brocken is a reservoir, the Brockenteich, constructed in 1744.
This is due to its short summers and very long winters, with many months of continuous snow cover, strong storms and low temperatures even in summer.
The summit, however, does not have an alpine climate, as the average summer temperature is above 10 °C (50 °F).
The Brocken, also sometimes referred to as the Blocksberg, is the highest peak of the Harz mountain range and also the highest peak of Northern Germany; it is located near Schierke in the German state of Saxony-Anhalt between the rivers Weser and Elbe.
Although its elevation of 1,141 metres (3,743 ft) is below alpine dimensions, its microclimate resembles that of mountains of about 2,000 m (6,600 ft).The peak above the tree line tends to have a snow cover from September to May, and mists and fogs shroud it up to 300 days of the year.The mean annual temperature is only 2.9 °C (37.2 °F).It is the easternmost mountain in northern Germany; travelling east in a straight line, the next prominent elevation would be in the Ural Mountains in Russia.The Brocken has always played a role in legends and has been connected with witches and devils; Johann Wolfgang von Goethe took up the legends in his play Faust.They originated mainly under periglacial conditions, i.e.