Subject: How does presence of impurities/ slight impurities interfere in crystal ?

Re: How does the presence of impurities/ slight impurities interfere ?
How does the presence of slight impurities interfere with the formation of 
a crystalline solid ?
i was bufled by a student's presentation on a crystal of 0.05% methylene 
blue with Barium nitrate crystal . 
can anyone tell me how the crystalline system change with the addition of 
impurities ?

For example , a crystal of pure barium nitrate is cubic in shape and the 
crystal with 0.05% methylene blue  produced an octahedral shaped crystal y 
is that so ?
my student in his presentation stated that the crystal forms in this way :

a few layers of an ionic lattice of Ba(NO3)2 will form first followed by 
the a " chains " of hydrogen bonded Methylene blue will settle onto the 
lattice resulting as fine ridges on the crystal surface .

I am still buffled by Y such things happened .
majority of the prof. i've asked were material physics majors and i 
specialised in chemical kinematics 

anyone out there with a chem major can help ? 
:)

Re: How does presence of impurities/ slight impurities interfere in crystal ?