tectosilicates and miscellaneous silicates in thin section


Check out the video atlas of minerals in thin section introduction page for some background on how these videos were prepared and processed, and for additional useful information on the included table content, the search tab, and other user-adjustable features. There is also an accompanying illustration to assist viewers with determining 2V° values from the BxA or optic axis figures in the “optic figures” videos.

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The Vimeo-hosted versions of these video are also search-engine discoverable, and can be found by searching for the term “thin section” coupled with the sample number (e.g. “thin section FKM-49”), with or without also including the accompanying mineral name. YouTube-hosted versions of these videos are no longer search-engine discoverable (in protest of YouTube polluting even short educational videos with non-optional ads… grrr!), but can still be found organized in playlists on my rockPTX YouTube channel.


mineral PPL (lower
polar rotation)
(stage rotation)
(stage rotation)
optic figure
(stage rotation)
quartz (FKM-15):
quartz in blueschist facies ferruginous meta-quartzite, with spessartine garnet
sanidine (FKM-80):
sanidine (K-feldspar) in haüyne phonolite, with aegirine clinopyroxene
orthoclase (FKM-78):
orthoclase micro-mesoperthite in high grade low-silica feldspathic gneiss, with biotite
microcline (FKM-74):
microcline K-feldspar in carbonatite-associated K-metasomatite, with diopside clinopyroxene, zoned amphibole and apatite
microcline (FKM-315):
microcline in metamorposed agpaitic syenite, with omphacite/aegirine-augite clinopyroxene and mosandrite-(Ce)
old video with especially distracting stray polarization effects scheduled to be replaced
albite (FKM-358):
essentially untwinned albite feldspar in high-grade Mn metasomatite, with rhodonite and aegirine clinopyroxene
“andesine” (plagioclase) (FKM-425):
“andesine” plagioclase feldspar in Ca-contaminated granite, with microcline/orthoclase K-feldspar, quartz, minor apatite and “myrmekite” (intergrowth with quartz)
anorthite (FKM-24):
anorthite (An95) plagioclase feldspar in high grade amphibolite, with tschermakite amphibole
reedmergnerite (FKM-52):
reedmergnerite feldspar in highly fractionated alkali granite, with quartz
maleevite (FKM-431):
maleevite in Cs-B-Li-enriched granite, with aegirine-augite, leucosphenite, alkali feldspar and quartz
“maskelynite” (FKM-325):
meteorite impact-associated “maskelynite” (plagioclase composition impact glass)
nepheline (FKM-77):
anomalously slightly biaxial nepheline in kakortokite, with albite plagioclase and eudialyte
nepheline (FKM-120):
nepheline in miaskitic nepheline syenite, with alkali feldspar, cancrinite and calcite
nepheline (FKM-146):
anomalously slightly biaxial nepheline in agpaitic nepheline syenite (“lakarpite”), with arfvedsonite amphibole and apatite
nepheline (FKM-218):
nepheline in leucite nephelinite, with diopside clinopyroxene and leucite
nepheline (FKM-342):
nepheline in carbonatite-associated wollastonite nephelinite, with [associated minerals]
kalsilite (FKM-271):
slightly altered Fe3+-bearing (0.29 to 0.40 Fe3+ apfu per ∑T=4.00) kalsilite in pyrometamorphic sanidinite facies phosphatic metacarbonate, with andradite garnet, gehlenite melilite, wollastonite and apatite (note: thin section is slightly thick)
leucite (FKM-218):
anomalously biaxial leucite in leucite nephelinite, with diopside clinopyroxene and nepheline
nosean (FKM-7):
nosean in nosean phonolite
haüyne (FKM-313):
haüyne in haüyne tephritic phonolite, with Na-sanidine (K-feldspar), plagioclase and diopside clinopyroxene
lazurite (FKM-25):
lazurite in granulite facies calcareous meta-evaporite, with calcite, phlogopite, diopside and nepheline (note: thin section is cut substantially thin)
isotropic (minor birefringent areas may be admixture with non-isometric polymorphs)
genthelvite (FKM-282):
genthelvite in granite, with albite, orthoclase and biotite
danalite (FKM-401):
danalite in Be-bearing Fe-metasomatite, with fluorite, biotite and ferro-pargasite amphibole
tugtupite (FKM-352):
tugtupite in agpaitic nepheline syenite, with ussingite
ye’elimite (FKM-383):
ye’elimite in sanidinite-facies paralava, with srebrodolskite, gehlenite and larnite
cancrinite (FKM-120):
cancrinite in miaskitic nepheline syenite, with plagioclase, nepheline and calcite
cancrinite (FKM-346):
cancrinite in agpaitic nepheline syenite, with alkali feldspar, nepheline and aegirine clinopyroxene
marialite (FKM-360):
marialite in alkali-chloride metasomatite, with [Mn+Fe]-bearing clinozoisite and calcite
meionite (FKM-165):
meionite (“wernerite”; 1.90 Na apfu; 1.84 Ca apfu) scapolite in crustal “carbonatite”, with calcite and titanite
ussingite (FKM-60):
ussingite in late pegmatite in agpaitic syenite
ussingite (FKM-352):
ussingite in agpaitic syenite, with albite
stilbite (FKM-170):
stilbite in zeolite facies altered basalt
hsianghualite (FKM-388):
hsianghualite in granite-associated phlogopite skarn, with phlogopite and fluorite

non-silicates in thin section

nesosilicates in thin section

sorosilicates and cyclosilicates in thin section

single chain inosilicates in thin section

double chain and more complex inosilicates in thin section

phyllosilicates in thin section