- Chemistry: Ca2ZnSi2O7
, Calcium Zinc Silicate.
- Class: Silicates
- Subclass: Sorosilicates
- Group: Melilite
- Uses: A very minor ore of zinc and as mineral specimens.
Hardystonite is well known to collectors of fluorescent minerals from
Franklin and Sterling Hill,
It will fluoresce a dark purple under short-wave ultraviolet
This fluorescent color is in striking contrast to the normal color
Fluorescence occurs when the ultraviolet light (invisible
to humans) imparts energy to some of the atoms in the mineral. This energy
is converted by the atom into visible light that we can then see. Hardystonite
is usually a dull, unattractive white, but under short-wave UV light it
The following table shows the more common fluorescing
minerals from Franklin and Sterling Hill, New Jersey.
These minerals are sometimes found in association with each other and
can make for wonderfully colorful fluorescent specimens. The violet-blue
color of hardystonite really stands out among these minerals. The combination
of hardystonite, clinohedrite and willemite is considered a mineralogical classic.
Hardystonite is a product of the metamorphism of zinc minerals, probably
that were caught up in the regional metamorphism that created the Franklin
site. Hardystonite is found no where else.
- Color is white to less commonly pale pink or brown.
- Luster is vitreous to dull.
- Transparency: Specimens are translucent to opaque, rarely transparent.
- Crystal System is tetragonal.
- Crystal Habits include massive and granular specimens.
- Cleavage is perfect in two directions and fair in two other
directions (all prismatic).
- Hardness is 3 - 4.
- Specific Gravity is approximately 3.4+ (above average)
- Streak is white.
- Other Characteristics: Fluoresces a dark violet to blue color
under short-wave UV light and no fluorescence under long-wave UV light.
- Associated Minerals include willemite,
and especially clinohedrite.
- Notable Occurrence is limited to its type locality: North Hill
Mine, Franklin, Sussex County, New Jersey, USA.
- Best Field Indicators are fluorescence, associations, locality