Crushed stone (aggregate)
Geologic features

This xenolith is the country rock into which the granite was intruded. The xenolith is a quartz-biotite gneiss. Note geologist for scale.

 

 

 

 

 

 

Quarries oftentimes are good opportunities to observe other geologic features.

When granitic rock intrudes the country rock it may include block of the country rock (left). This feature is called a xenolith. This particular rock is a quartz-biotite gneiss. This field observation shows that the country rock (xenolith) is older than the granite. Field observations like this help develop the geologic history and sequence of events.

Another feature seen in the same quarry is a dike (below). The dike intrudes the granite and cross cuts the granites foliation. This cross cutting relationship proves the dike is younger than the granite and the events that affected it.

One interpretation of geologic history at this quarry is deposition of the country rock, its metamorphism (the biotite gneiss), intrusion of the granite, and finally intusion of the dike.

Cross cutting dike intrudes foliated granite. The dike is several feet wide.