tuch
A dark-coloured kind of marble; touchstone.

tugarinovite
A monoclinic-prismatic violet brown mineral containing molybdenum and oxygen.

tuhualite
An orthorhombic-dipyramidal mineral containing iron, oxygen, potassium, silicon, and sodium.

tuite
A trigonal-ditrigonal pyramidal mineral containing calcium, iron, magnesium, oxygen, phosphorus, and sodium.

tulameenite
A tetragonal-ditetragonal dipyramidal white mineral containing copper, iron, and platinum.

tuliokite
A trigonal-rhombohedral mineral containing barium, carbon, hydrogen, oxygen, sodium, and thorium.

tumchaite
A monoclinic-prismatic colorless mineral containing hydrogen, oxygen, silicon, sodium, tin, and zirconium.

tunellite
A monoclinic-prismatic colorless mineral containing boron, hydrogen, oxygen, and strontium.

tungstenite
The mineral now known as scheelite

tungstibite
An orthorhombic-disphenoidal mineral containing antimony, oxygen, and tungsten.

tungusite
A triclinic-pinacoidal mineral containing aluminum, calcium, hydrogen, iron, magnesium, manganese, oxygen, silicon, and sodium.

tunisite
A tetragonal-ditetragonal dipyramidal mineral containing aluminum, calcium, carbon, chlorine, hydrogen, oxygen, and sodium.

tuperssuatsiaite
A red-brown monoclinic mineral comprising mostly iron, silicon, and oxygen.

turanite
An olive green mineral containing copper, hydrogen, oxygen, and vanadium.

turgite
A ferric hydrate, 2Fe₂O₃H₂O, closely related to hematite and limonite.

turgites
plural of turgite

turjaite
A type of melilitolite containing more than 10% nepheline.

turjaites
plural of turjaite

turjite
Alternative form of turjaite.

turjites
plural of turjite

turkestanite
A tetragonal-ditetragonal dipyramidal mineral containing calcium, hydrogen, oxygen, potassium, silicon, sodium, and thorium.

turnerite
A variety of monazite with golden yellow to brownish yellow crystals.

turquoises
plural of turquoise

turtmannite
A trigonal-hexagonal scalenohedral mineral containing arsenic, hydrogen, magnesium, manganese, oxygen, silicon, and vanadium.

tuscanite
A monoclinic-prismatic colorless mineral containing aluminum, calcium, carbon, hydrogen, iron, magnesium, oxygen, potassium, silicon, sodium, and sulfur.

tusionite
A rare trigonal borate mineral.

tuzlaite
A monoclinic-prismatic mineral containing boron, calcium, hydrogen, oxygen, and sodium.

tvalchrelidzeite
A grey mineral containing mercury, antimony, arsenic, and sulfur.

tvedalite
An orthorhombic mineral containing beryllium, calcium, hydrogen, manganese, oxygen, and silicon.

tweddillite
A mineral containing calcium, strontium, manganese, aluminum, oxygen and hydrogen, found in Japan, Italy and South Africa.

twinnite
A triclinic-pinacoidal black mineral containing antimony, arsenic, lead, and sulfur.

twoer
A glass marble in children's games, slightly larger and more valuable than a oner.
A conker that has won two matches.

twoers
plural of twoer

twoling
A twin crystal consisting of two individuals.

twolings
plural of twoling

tychite
An isometric-diploidal mineral containing carbon, magnesium, oxygen, sodium, and sulfur.

tyretskite
A triclinic-pedial mineral containing boron, calcium, hydrogen, and oxygen.

tyrrellite
An isometric-hexoctahedral bronze mineral containing cobalt, copper, nickel, and selenium.

tysonite
fluocerite

tysonites
plural of tysonite

tyuyamunite
A very rare uranium mineral, Ca(UO₂)₂V₂O₈·(5-8)H₂O.

tyuyamunites
plural of tyuyamunite

tyuyamuyunite
Alternative form of tyuyamunite.

uakitite
An isometric mineral containing vanadium and nitrogen.

uhligite
A black isometric mineral containing aluminium, calcium, oxygen, titanium and zirconium.

uigite
A variety of chlorastrolite found on the island of Skye.

ulexite
A white mineral with triclinic crystals, NaCaB₅O₉·8H₂O, noted for its fibers which transmit light by internal reflection, such that a piece with flat faces perpendicular to the fibers' orientation displays an image of whatever is adjacent to its other side.

ulexites
plural of ulexite

ultramelilitolite
A melilitolite with more than 65% melilite.

ulvite
ulvöspinel

umagite
A mineral selenide of copper Cu₃Se₂

umangite
A selenide mineral, with chemical formula Cu₃Se₂, blue to red in color.

umbozerite
An amorphous mineral containing hydrogen, oxygen, silicon, sodium, strontium, and thorium.

umohoite
A triclinic-pinacoidal mineral containing hydrogen, molybdenum, oxygen, and uranium.

umohoites
plural of umohoite

umptekite
A syenitic rock consisting of microperthite, arfvedsonite, aegirine and, possibly, nepheline.

umptekites
plural of umptekite

underburden
To give too light a burden; to assign less than a fair share.
To assign less work than someone or something is capable of.

underburdens
plural of underburden

underclay
A stratum of clay lying beneath a coal bed.

ungaite
A variety of dacite containing oligoclase.

ungarettiite
A monoclinic-prismatic mineral containing manganese, oxygen, silicon, and sodium.

ungemachite
A trigonal-rhombohedral mineral containing hydrogen, iron, nitrogen, oxygen, potassium, sodium, and sulfur.

unionite
A form of zoisite

unisilicate
A salt of orthosilicic acid where the ratio of oxygen atoms united to the basic metals and silicon respectively is 1:1.

unisilicates
plural of unisilicate

upalite
A monoclinic mineral containing aluminium, uranium, oxygen, phosphorus, and hydrogen.

uralborite
A monoclinic-prismatic colorless mineral containing boron, calcium, hydrogen, and oxygen.

uralite
A dark green variety of hornblende or actinolite.

uralites
plural of uralite

uralolite
A monoclinic-prismatic mineral containing beryllium, calcium, hydrogen, oxygen, and phosphorus.

uramphite
A tetragonal-ditetragonal dipyramidal mineral containing hydrogen, nitrogen, oxygen, phosphorus, and uranium.

urancalcarite
An orthorhombic bright yellow mineral containing calcium, carbon, hydrogen, oxygen, and uranium.

uranmicrolite
An isometric-hexoctahedral mineral containing calcium, hydrogen, niobium, oxygen, tantalum, and uranium.

uranocircite
A tetragonal-ditetragonal dipyramidal mineral containing barium, hydrogen, oxygen, phosphorus, and uranium.

uranopissite
Synonym of uraninite.

uranopolycrase
An orthorhombic-dipyramidal brown red mineral containing niobium, oxygen, tantalum, thorium, titanium, uranium, and yttrium.

uranosilite
An orthorhombic-disphenoidal yellowish white mineral containing oxygen, silicon, and uranium.

uranospathite
An orthorhombic-pyramidal mineral containing aluminum, fluorine, hydrogen, oxygen, phosphorus, and uranium.

uranotil
Archaic form of uranotile.

uranotile
Synonym of uranophane.

uranotiles
plural of uranotile

uranotungstite
An orthorhombic mineral containing barium, hydrogen, iron, lead, oxygen, tungsten, and uranium.

uranpyrochlore
An isometric-hexoctahedral mineral containing calcium, cerium, fluorine, hydrogen, niobium, oxygen, tantalum, and uranium.

urao
The mineral trona.

urbainite
A mineral consisting mainly of ilmenite, hematite, and rutile.

ureilite
An achondrite composed mostly of olivine and clinobronzite with some diamond or graphite.

ureyite
Synonym of kosmochlor.

uricite
A monoclinic-prismatic mineral containing carbon, hydrogen, nitrogen, and oxygen.

ursilite
An orthorhombic mineral containing calcium, hydrogen, magnesium, oxygen, silicon, and uranium.

urusovite
A monoclinic-prismatic light green mineral containing aluminum, arsenic, copper, and oxygen.

urvantsevite
A tetragonal-ditetragonal dipyramidal steel gray mineral containing bismuth, lead, and palladium.

ushkovite
A triclinic-pinacoidal mineral containing hydrogen, iron, magnesium, oxygen, and phosphorus.

usovite
A monoclinic mineral containing aluminum, barium, calcium, fluorine, and magnesium.

ustarasite
An orthorhombic pure white mineral containing antimony, bismuth, lead, and sulfur.

utahite
A triclinic mineral containing copper, hydrogen, oxygen, tellurium, and zinc.

utahlite
Synonym of variscite.