Granites and Quartz
"Alaskan White Granite" is not from Alaska. It is a porphyritic garnetiferous leucogranite from the Ordovician of Brazil. This rock has plagioclase feldspar, quartz, mica, potassium feldspar, and garnet.
A graphic granite attributed to Brazil with creamy-colored potassium feldspar, gray quartz, and a mafic mineral (probably biotite mica).
Granite from the Precambrian-Cambrian of Brazil. "Granite" in the decorative stone trade is any relatively hard rock that will take a fine polish, regardless of mineralogy or chemistry or geologic origin. "Granites" turn out to be felsic to mafic intrusive igneous rocks (granite, granodiorite, porphyritic granite, rapakivi granite, orbicular granite, pegmatitic granite, graphic granite, anorthosite, monzonite, gabbro, norite, gabbronorite, dolerite, diabase, charnockite, etc.) and high-grade to very high-grade metamorphic rocks (metanorthosite, gneiss, metaconglomerate, amphibolite, quartzite, granulite, migmatite).
Sodalite metasyenite from the Precambrian of Brazil. "Azul Bahia Granite" from eastern Brazil has the reputation for being a very expensive decorative stone. It's distinctive in having considerable non-iridescent blue coloration.
Azurite Orbs in Granite
This unusual rock is ordinary granite but has scattered subspherical masses of bluish-colored azurite (Cu3(CO3)2(OH)2 - copper hydroxy-carbonate). Minor greenish-colored malachite is also present (Cu2CO3(OH)2). The granite is composed of quartz (SiO2), microcline feldspar (KAlSi3O8), albite feldspar (NaAlSi3O8), and mica.
Rapakivi granite from the Precambrian of Finland. Baltic Brown Granite is a variety of rapakivi granite called wiborgite, characterized by having large K-feldspar spheroids rimmed (usually) by greenish plagioclase feldspar. Wiborgite is composed of K-feldspar, plagioclase feldspar, quartz, biotite mica, and hornblende amphibole. This rock comes from the Wiborg Batholith (a.k.a. Wiborg Rapakivi Granite Batholith, Wiborg Massif, Vyborg Batholith) in the Baltic Shield (Fennoscandian Shield).
A rapakivi granite from southern Finland. This variety of rapakivi granite is called pyterlite. Pyterlite is characterized by having large K-feldspar spheroids that usually lack rims of greenish plagioclase feldspar. So, wiborgite has common plagioclase rims, and pyterlite commonly lacks plagioclase rims. The pyterlite sample shown here has one K-feldspar spheroid at the upper left with a greenish-brown plagioclase feldspar rim. Pyterlite is composed of reddish K-feldspar, greenish-brown plagioclase feldspar, dark-grayish quartz, and black biotite mica. This rock comes from the Wiborg Batholith (a.k.a. Wiborg Rapakivi Granite Batholith, Wiborg Massif, Vyborg Batholith) in the Baltic Shield (Fennoscandian Shield).
A Precambrian norite from Quebec, Canada. Geologic unit & age: Lac-St.-Jean Anorthosite Suite, late Mesoproterozoic, 1.14 to 1.16 b.y. Locality: quarry at St. Nazaire, Chicoutimi County, southern Quebec, southeastern Canada.
A Proterozoic-aged norite from India’s Eastern Ghats Orogenic Belt. This is probably the most popular and attractive black granite available in the commercial decorative stone trade. It has blackish plagioclase feldspar and bronzite pyroxene crystals. Bronzite is an orthopyroxene and it has a spectacular copper-colored play of color on cut & polished surfaces (even on broken surfaces). The result is a rock surface reminiscent of sparkling stars in space, hence the commercial name "Black Galaxy". This rock is quarried in the Chimkurthi area, Prakasam District, Andhra Pradesh State, southern India.