Round framgents cemented together

The rock formed is very hard and resistant to be worn down.
The following parts can be distinguished: the weft, (fragments greater than 2 mm) forming the frame; the matrix (sands) that fills the gaps between the big fragments of the weft; and the cement, which joins the various fragments.
The edges may come from the erosion of any type of rock.

It involves an intense process of transport and erosion by the water, which rounds the fragments of the rocks 

Its purple-pink colour (typical of amethysts) offer different shades depending on the angle at which they are exposed to light. They can be completely filled with the minerals that have precipitated into the walls of the cavity or there can be a hollow space inside.

They usually occur when the gases become trapped and remain in the rock leaving a hole inside or by the dissolution of the adjacent rocks. The process of formation of the geodes is produced during the cooling of the magma. The minerals that precipitate to form the Geode reach it dissolved in the water 

It is a non-foliated

metamorphic rock and 

it is used to make columns, statues and if it is polished it is for worktops and grounds of houses. 

I found it in the Plaza Zorrila, in the statue of José Zorrilla. 

It is a igneous rock and intrusive. 

And the amount of mica I think too.

It seems GNEISS, THE FOLLOWING STAGE in the metamorphic process. In gneiss mineral grains have grown a lot, ones feeding the others (the teacher)