For the explanation of the conditions of pressure and of temperature at the emergence of agates are agates, whose formation clearly within the diagenetic range (standard temperature and - pressure ratios) took place. A good example for this is this amber from Kuji, which belongs to the collections of the amber cabinet of the museum at theLoewentor in Stuttgart.
…Japanese amber of Kuji with approx. 13% quartz portion, 87% amber; double as big as a fist. That breaking into is many heavier than usual, because he contains a quantity of quartz minerals in the form of irregular lenses and countless lines. Obviously the piece (perhaps by earthquakes) had been destroyed completely and stuck together by the penetrating quartz solutions! Now it is completely stable; the quartz is to be seen direct, and one can calculate it by the specific weights of amber and quartz. When sawing one could hear crashes (!), where one discovered the quartz fillings quartz and when polishing stepped somewhat out (...) the lines, i.e. the sticking together joints, contains white quartz without special characteristics, the different colored banding parts are representing the agate structure. Such pieces with many veins running all over occur in Kuji and Iwaki in large number. Usually they are however rather inconspicuous. Our issued piece, which we owe to Mr. Y.Morita, is because of its spherical shape and the even, netlike tear distribution and the small agates inside the most beautiful specimen which I saw. It demonstrates also the strange fact that the surface of the piece of amber is not covered by a quartz crust by any means. Only inside the veins and cavities were the conditions such a like that the quartz solution could begin to crystallize ….
Source: Dieter Schlee, the amber cabinet, handbook to the amber exhibition in the museum at the lion gate Stuttgart, Stuttgart contributions to the natural history, ISSN 0341-0161
A further similar piece with the discovery site Golling, Austria belongs likewise to the Collection of the amber cabinet.
This is the link to the website of the Loewentor museum in Stuttgart.