THE MINERAL BERLINITE
Berlinite is a rare phosphate mineral first discovered at the Vestana iron mine, Nastum, Sweden. It would not be very outstanding except for the fact that it is the only known mineral to be isostructural with quartz. Isostructural means that they have the same structure although the two minerals have rather different chemistries. Quartz, SiO2, would seem to be very different from berlinite, AlPO4. But if the formula of quartz is written as SiSiO4 then the similarity is obvious.
The reason that berlinite is able to have the same structure as quartz is because the aluminum and phosphorus ions are of similar size to silicon ions. Thus the same structure can be achieved since the aluminums and phosphorus can completely replace the silicons without alteration of the quartz structure. Unfortunately, berlinite rarely forms crystals. It would be fascinating to compare the crystals of berlinite to those of quartz.
- Color is colorless, gray to pink or rose.
- Luster is vitreous.
- Transparency: Crystals are transparent to translucent.
- Crystal System is trigonal; 3 2
- Crystal Habits include granular masses and disseminated grains.
- Cleavage is absent.
- Fracture is conchoidal.
- Hardness is 6.5
- Specific Gravity is approximately 2.6 (average for translucent minerals)
- Streak is white or gray.
- Notable Occurrences include the Vestana iron mine, Nastum, Sweden.
Best Field Indicators are locality, color, absence of cleavage and hardness.