THE MINERAL HODGKINSONITE

Chemistry: Zn₂MnSiO₄(OH)₂, Zinc Manganese Silicate Hydroxide.
Class: Silicates
Subclass: Nesosilicates
Group: Euclase
Uses: A very minor ore of zinc and as mineral specimens.
Specimens

Hodgkinsonite is one of several minerals that come from Franklin and Sterling Hill, New Jersey and no where else! It is a product of the metamorphism of zinc minerals, such as hemimorphite and/or smithsonite, that were caught up in the regional metamorphism that created the wonderful Franklin and Sterling Hill sites. Its structure is composed of manganese hydroxide sheets, lnterlayered with sheets of zinc and silicate tetrahedrons. The sheet like structure gives it its perfect basal cleavage.

Hodgkinsonite is named after H. H. Hodgkinson, whom discovered the mineral in 1913. Hodgkinsonite is a very attractive mineral and has even been cut as a gemstone. It has a bright pink to lavender color that is similar to rhodonite, but not quite as red. Hodgkinsonite is most known for its association with snow white barite crystals in veins that cut through the ores composed of willemite and franklinite. It has even been associated with native copper. The attractiveness and color along with the associated minerals have made hodgkinsonite a favorite with collectors of Franklin minerals. Unfortunately the mines have all but completely closed and therefore the only source of hodgkinsonite is material that has already been collected.

PHYSICAL CHARACTERISTICS:

Color is lavender, violet, pink, brown, yellow, orange to black.
Luster is vitreous.
Transparency: Specimens are transparent to translucent.
Crystal System is monoclinic; 2/m.
Crystal Habits include blocky to stubby prismatic crystals. Microcrystals display a acutely sharp pyramidal crystal form. Also massive and vein filling.
Cleavage is perfect in one direction (basal).
Hardness is 4.5 - 5.
Specific Gravity is approximately 3.9 (above average)
Streak is white.
Other Characteristics: Does not fluoresce often, but some specimens have shown a red fluorescence under longwave UV light.
Associated Minerals include barite, willemite, zincite, tephroite, pyrochroite, spessartine, copper, franklinite, calcite and descloizite.
Notable Occurrences are limited to its type locality: Franklin and Sterling Hill, New Jersey, USA.
Best Field Indicators are locality, color, crystal habit, cleavage and associations.