Nuummite
Nuummite is a gemstone formed from a mixture
of two minerals from the orthoamphibole group: anthophyllite
and gedrite. The name nuummite is derived from the Municipality
of Nuuk, where the stone was discovered in 1982. It
has since been found in several localities in the outer part
of the Godthabsfjord near Nuuk.
Geologically speaking, nuummite is of volcanic
origin and was formed about 3 billion years ago. Subsequent
influences on the rock (metamorphism) have given rise to the
striking mixture of crystals which gives nuummite its unique
appearance. Rocks resembling nuummite are also found
in a few minor occurrences in the USA, but it is only in the
Greenland type that coloration is developed well enough for
the stone to be suitable for gemstones.
Composition
 In
nuummite, the two orthoamphibole, anthophyllite (Mg,Fe)7Si8O22(OH)2
and gedrite (Mg,Fe)5Al2(Al,Si)8O22(OH)2,
both with a hardness of 5 to 5.6, constitute a mixture of
elongated crystals, often in sheaf-like groups. In the
transition between the individual crystals (and especially
the thin ones), an optical effect is created causing a special
“inner” golden brown glow. This effect is
also called iridescence, and is especially distinct on polished
surfaces. The result is that the crystals appear as bright
lamellae, almost like flames in a fire. The colors vary
somewhat between reddish, greenish, and bluish hues, sometimes
even within the same lamella. Between the bright lamellae,
the color is dark brown to black.
Gemstone
 Nuummite
is generally easy to polish, even though, in certain qualities
of stones with many parallel crystals, it can be difficult
to avoid holes and cracks. The usual shape is cabochon,
but other convex finishes also produce pleasing results.
In larger pieces it is possible to retain most of the colors
of the iridescence, so that one end of the cabochon has a
golden hue while the opposite end has a bluish tone.
Nuummite is well suited to mounting in both gold and silver.
MinerShop stocks an inventory
of this and other Gem Rough. Contact
sales for availability and prices.
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