Tremolite

inosilicate

metamorphic

Formula: ☐Ca2(Mg5.0-4.5Fe2+0.0-0.5) Si8O22(OH)2
Inosilicate (chain silicate) amphibole
Specific gravity: 2.99 to 3.03
Hardness: 5 to 6
Streak: White
Colour: Green, white, brown
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Metamorphic environments (common)

Tremolite is an amphibole. It is an important rock-forming mineral and occurs most commonly as a component of metamorphosed carbonate rocks, especially skarn and dolomite marble, where the crystals and aggregates can be quite large. In this environment it commonly forms as pseudomorphs of tremolite after diopside, but it can also be primary. Tremolite is common in many metamorphosed mafic and ultramafic rocks such as amphibolite, although actinolite and other iron-rich amphiboles usually dominate there.
Tremolite also may be found in skarn
It is a mineral of the albite-epidote-hornfels, hornblende-hornfels, greenschist, amphibolite and granulite facies.

Alteration

During the progressive metamorphism of silica-rich dolostones the following approximate sequence of mineral formation is often found, beginning with the lowest temperature product: talc, tremolite, diopside, forsterite, wollastonite, periclase, monticellite

diopside, CO2 and H2O to tremolite, calcite and quartz
5CaMgSi2O6 + 3CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with dolomite
(DHZ 2A p276)

diopside and antigorite to forsterite, Mg-rich tremolite and H2O
2CaMgSi2O6 + 5Mg3Si2O5(OH)4 ⇌ 6Mg2SIO4 + Ca2Mg5Si8O22(OH)2 + 9H2O
At 10 kbar pressure the equilibrium temperature is about 580oC (amphibolite facies)
(SERC)

diopside, dolomite, CO2 and H2O to tremolite and calcite
4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3
Diopside is produced by the metamorphism of siliceous dolostone, and if water is introduced at a later stage tremolite may be produced from the above reaction, or by the reaction of diopside with CO2 and H2O
(DHZ 2A p276)

dolomite, quartz and H2O to tremolite, calcite and CO2
5CaMg(CO3)2 + 8SiO2 + H2O → Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2
This is a metamorphic reaction in dolomitic limestone
(MOM p496)

dolomite and tremolite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O
(DHZ 5B p213)

dolomite, tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At a pressure of 4 kbar the equilibrium temperature is about 840oC (granulite facies)
(JVW p97)

serpentine and diopside to tremolite, forsterite and H2O
5Mg3Si2O5(OH)4 + 2CaMgSi2O6 ⇌ Ca2Mg5Si8O22(OH)2 + 6Mg2SiO4 + 9H2O + H2O
In lower grade assemblages associated with contact and regional metamorphism serpentine may form tremolite and forsterite according to the above reaction
(DHZ 2A p271)

spinel and tremolite to forsterite and magnesio-hornblende MgAl2O4 + Ca2Mg5Si8O22(OH)2 ⇌ Mg2SiO4 + Ca2(Mg4Al)(Si7Al)O22(OH)2
This reaction occurs in some strongly metamorphosed serpentinite
(DHZ 1A p261)

talc and calcite to tremolite, dolomite, CO2 and H2O
2Mg3Si4O10(OH)2 + 3CaCO3 +4SiO2 → Ca2Mg5Si8O22(OH)2 + CaMg(CO3)2 + CO2 +H2O
This is a low-grade metamorphic change, occurring at temperature between about 250oC and 450oC
(MOM)

talc, calcite and quartz to tremolite, CO2 and H2O
5Mg3Si4O10(OH)2 + 6CaCO3 +4SiO2 → 3Ca2Mg5Si8O22(OH)2 + 6CO2 +2H2O
Metamorphism of siliceous carbonate rock causes the formation of hydrous phases such as talc and tremolite
(DHZ 5B p127)

talc, calcite and quartz to tremolite, CO2 and H2O
5Mg3Si4O10(OH)2 + 6CaCO3 +4SiO2 → 3Ca2Mg5Si8O22(OH)2 + 6CO2 +2H2O
(DHZ 5B p127, p213)

tremolite to diopside, enstatite, quartz and H2O
Ca2Mg5Si8O22(OH)2 ⇌ 2CaMgSi2O6 + 3MgSiO3 + SiO2 + H2O
At temperatures of 575oC and above tremolite is unstable and alters to diopside and enstatite.
The equilibrium temperature for this reaction at 8 kbar pressure is 930oC (granulite facies), with the equilibrium to the right at higher temperatures, and to the left at lower temperatures (for the same pressure)
(KB p421, diagram p420, SERC)

tremolite and CO2 to dolomite, talc and SiO2
☐Ca2Mg5Si2O22(OH)2 + CO2 ⇌ 2CaMg(CO3)2 + Mg3Si4O10(OH)2 + 4SiO2
In the greenschist facies tremolite may be converted to talc according to the above reaction
(DHZ 3 p127)

tremolite, anorthite and clinochlore to tschermakite and H2O
3☐Ca2MgSi8O22(OH)2 + 8Ca(Al2Si2O8) + 2Mg5Al(AlSi3O10)(OH)8 ⇌ 5☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2 + 4H2O
(AM 76.998)

tremolite and calcite to diopside, dolomite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 ⇌ 4CaMgSi2O6 + CaMg(CO3)2 + CO2 + H2O
The forward reaction is a diopside-forming metamorphic reaction
(DHZ 2A p249)

tremolite, calcite and quartz to diopside, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO2 → 5CaMgSi2O6 + 3CO2 + H2O
This is a medium-grade metamorphic change occurring at temperature between about 450oC and 600oC
(DHZ 2A p270, MOM)

tremolite and dolomite to forsterite, calcite, CO2 and H2O
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3)2 → 8Mg2SiO4 + 13CaCO3 + 9CO2 + H2O
(DHZ 1A p264)

tremolite, dolomite and H2O ⇆ hydroxylclinohumite, calcite and CO2
Ca2Mg5Si8O22(OH)2 + 13CaMg(CO3)2 + H2O ⇌ 2(4Mg2SiO4.Mg(OH)2) + 15CaCO3 + 11CO2

tremolite and forsterite to diopside, enstatite and H2O
Ca2Mg5Si8O22(OH)2 + Mg2SiO4 ⇌ 2CaMgSi2O6 + H2O
At 4 kbar pressure the equilibrium temperature is 840oC (granulite facies)
(JVW p97)

tremolite, tschermakite and albite to pargasite and quartz
☐Ca2Mg5Si8O22(OH)2 + ☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2 + 2Na(AlSi3O8) ⇌ 2NaCa2(Mg4Al)(Si6Al2)O22(OH)2 + 8SiO2
(AM 92.4.491)

tremolite, zoisite, corundum and H2O to tschermakite
3☐Ca2MgSi8O22(OH)2 + 2Ca2Al3[Si2O7][SiO4]O(OH) + 7Al2O3 + H2O ⇌ 5☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2
(AM 76.990)

Common impurities: Ti,Mn,Al,Na,K,F,Cl,H2O

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