#pegmatite
All of these samples were collected at Hogen Camp Mine, Harriman State Park, NY. The first image is a reflected light image of the ore vein. The ore vein formed as a result of dextral shear which ultimately created large fractures. Shortly after this, hydrothemal alteraltion occured of the metavolcanic gneiss in the region (image 2 and 3). The metavolcanic gneiss is rich in iron. Due to this, the highly acidic metamorphic fluids began to precipitate in the fractures. The process yeilded magnetite, clinopyroxene, and less common biotite within the fractures occuring at Hogen Camp Mine. The clinopyroxene and biotite are highly rich in iron.
Image 3 and 4 is the local pink pegmatites that occured in the region around 923 Ma. The pegmatitic dikes formed post-Ottawan orogeny. Composition includes: alkali feldspar with minor constituents of clinopyroxene and quartz.
Norbergite
These yellow crystals bear testament to the forces of metamorphism, which transformed the original sea bottom limestone into glistening white marble, concentrating the impurities in the rock into gems. This particular one was magnesium rich, since the marble is dotted with red spinel crystals (magnesium aluminium oxide) along with a larger yellow-brown chunk of normbergite (hydrated fluorated magnesium silicate).
The specimen comes from the Mogok stone tract of Burma, source of the traditional pigeon’s blood ruby. The original limestone was transformed from sea bottom to land and limestone to marble by the collision of India with Eurasia that eliminated the eastern half of the near gone palaeoocean Tethys (the other half is but a sad remnant called the Mediterranean as Africa removes its last vesiges).
The mineral is named after its type location from which it was first scientifically described. Unlike the 4.9 x 2.9 x 1.7 cm Burmese example in the photo which was born in what is known as a regional metamorphic event (when a large area of land is transformed in belts that reflect variations in temperature and pressure conditions during a mountain building event), the original material from Norberg in Sweden came from a different kind of metamorphism called contact metamorphism, which occurs when existing rocks surrounding an intruding mass of molten rock rising from the bowels of the Earth are baked and stewed in the igneous juices. The granites (in this case) pushed into carbonate rocks and the last refined water rich remnants of the magma gave up its fluorine as a pegmatite.
The mineral fluoresces in UV light, as electrons are excited by the higher energy and wavelength rays and give up that energy after some time, emitting lower energy visible light wavelengths as it does so. Other sources include the Franklin mines in New Jersey, Canada, Finland and Italy. As well as the colour of the specimen, crystals can also be white, orange or red. The Mohs hardness weighs in at 6.5, between feldspar and quartz.
Loz
Image credit: Rob Lavinsky/iRocks.com
http://www.mindat.org/min-2925.html
http://bit.ly/1NItqgt
http://bit.ly/1KWJncT
http://www.galleries.com/Norbergite
