fire agate

{{short description|Variety of chalcedony with fire-like flashes}}

{{more citations|date=February 2025}}

{{Infobox mineral

| name = Fire agate

| category = Tectosilicate minerals, quartz group, chalcedony variety

| boxwidth =

| boxbgcolor =

| image = High Grade Slaughter Mountain Arizona Fire Agate Rough.jpg

| imagesize = 320px

| caption = Raw fire agate

| formula = Silica (silicon dioxide, SiO₂)

| molweight = 60 g / mol

| color = Red to orange, brown, iridescent flashes

| habit = Frequently botryoidal, microgranular aggregates

| system = Trigonal (quartz), monoclinic (moganite)

| twinning =

| cleavage = Absent

| fracture = Uneven, splintery, conchoidal

| mohs = 6.5-7

| luster = Waxy, vitreous

| refractive = 1.530 to 1.543

| opticalprop = Uniaxial (+)

| birefringence = 0.003 to 0.009

| pleochroism = None

| streak = White

| gravity = 2.60- 2.64

| density =

| melt =

| fusibility =

| diagnostic =

| solubility =

| diaphaneity = Translucent to opaque

| impurities = Iron oxides (limonite or goethite)

| references =

}}

Fire agate is a variety of chalcedony that displays fire-like iridescent flashes. It is found only in certain areas of central and northern Mexico and the southwestern United States (New Mexico, Arizona and California).{{Cite book |last1=Butler |first1=Gail A. |url=https://books.google.com/books?id=CusJV_D2ihwC&dq=%22fire+agate%22&pg=PA12 |title=Rockhounding California: A Guide to the State's Best Rockhounding Sites |last2=Koss |first2=Shep |date=2012-06-19 |publisher=Rowman & Littlefield |isbn=978-0-7627-8623-7 |pages=12–13 |language=en}} Despite its name, it is not a true agate, since it typically does not have bands.{{Cite web |title=Agate |url=https://www.mindat.org/min-51.html |access-date=2025-02-12 |website=www.mindat.org}} Approximately 24-36 million years ago, during the Tertiary Period,{{citation needed|date=February 2025}} these areas were subjected to massive volcanic activity. Fire agates were formed when hot water, saturated with silica and iron oxide, filled cracks and cavities in the surrounding rock and solidified into chalcedony layered with crystallized iron oxide.{{Cite web |title=Fire Agate {{!}} Gemstones.com |url=https://www.gemstones.com/articles/fire-agate |access-date=2025-02-12 |website=www.gemstones.com |language=en}}

Fire agates have beautiful iridescent rainbow colors, similar to opal. They have a hardness of 6.5-7 on the Mohs scale,{{Cite web |title=Fire Agate gemstone information |url=https://www.gemdat.org/gem-7601.html |access-date=2025-02-12 |website=www.gemdat.org}} which reduces the occurrence of scratching when polished gemstones are set in jewelry. The vibrant iridescent rainbow colors found within fire agates are created by the Schiller effect, which is also found in mother-of-pearl.{{citation needed|date=February 2025}} The brown color and iridescence of fire agates is due to inclusions of the iron oxides goethite or limonite.{{Cite web |title=Fire Agate |url=https://www.mindat.org/min-7601.html |access-date=2025-02-12 |website=www.mindat.org}}