I guess I'll play the GOSA petrologist too....
Althought granite can be black and white, in my experience this is seldom true.   Gneiss, which can form from the metamorphism of granite, also seldom occurs as a black and white rock.
Rhyolite is the volcanic equivalent of granite (although most rhyolites have a higher silica content than that of granites).  Rhyolites often ocurr in white or light gray colors, but can be black as black can be in the case of rhyolite obsidians.  Rhyolite is abundant at the geyser basins of Yellowstone.
I'm not suggesting the new feature at Biscuit Basin be named "Rhyolite Geyser".  There's got to be a better name out there assuming this feature stays around for a while. 
-Will
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We've had an awful lot of suggestions on here about different ways to say Black 
and White in a name.

Far be it from me to say anything uncondimentary about Salt and Pepper, or 
suggest that Granite isn't a gneiss name. When Scott first was brainstorming 
black-and-white possibilities and coming up only with banded onyx, I almost 
posted then to suggest Gneiss. Seeing the path the discussion has taken, it's 
time I say why I didn't.

In the case of thermal features named after ocean products like coral and pearl, 
rare precious stones like emerald, topaz, and beryl that aren't found anywhere 
near the park, manmade metals like bronze, and nonnative trees like ebony, it is 
abundantly clear that the thermal feature is named after it only because of an 
outward resemblence. 

On the other hand, there is real black sand near Black Sand Pool, real calcium 
carbonate at Calcite Springs, real arsenic sulfide (even if most of it isn't 
really realgar) at Realgar Spring, real sulfur at Sulfur Dust Pool, real glacial 
moraine at Till Geyser, a real dead mouse found floating in Peromiscus Spring 
once upon a time...

I am opposed to seeing a thermal feature named after a mineral (rock, fossil, 
tree,etc) which is found in the Yellowstone area (or is non-precious and common 
in some other area not too far away) unless the substance is actually present in 
the vicinity of the thermal feature.  I think names like Granite, Garnet, 
Gneiss, Feldspar, Tuff, Trilobite, would all make great names for a thermal 
feature SOMEWHERE -- but  no granite anywhere near Biscuit Basin.


