Editing Amber (section)

==Composition and formation==
Amber is [[Homogeneity and heterogeneity|heterogeneous]] in composition, but consists of several [[resin]]ous {{clarify span|text=bodies|reason=should this be replaced by "substances"?|date=March 2023}} more or less soluble in [[ethanol|alcohol]], [[diethyl ether|ether]] and [[chloroform]], associated with an insoluble [[Bitumen|bituminous]] substance. Amber is a [[macromolecule]] formed by free [[radical polymerization]]<ref name=Anderson2023>{{cite journal | last = Anderson | first = L.A. | year = 2023 | title = A chemical framework for the preservation of fossil vertebrate cells and soft tissues | journal = Earth-Science Reviews | volume = 240 | pages = 104367 | doi = 10.1016/j.earscirev.2023.104367 | bibcode = 2023ESRv..24004367A | s2cid = 257326012 | doi-access = free }}</ref> of several precursors in the [[labdane]] family, for example, [[communic acid]], [[communol]], and [[biformene]].{{sfn|Rudler|1911|p=792}}<ref>Manuel Villanueva-García, Antonio Martínez-Richa, and Juvencio Robles [http://www.arkat-usa.org/ark/journal/2005/I06_Juaristi/1567/EJ-1567C.asp Assignment of vibrational spectra of labdatriene derivatives and ambers: A combined experimental and density functional theoretical study] {{webarchive|url=https://web.archive.org/web/20060412074659/http://www.arkat-usa.org/ark/journal/2005/I06_Juaristi/1567/EJ-1567C.asp |date=12 April 2006 }} [[Arkivoc]] (EJ-1567C) pp. 449–458</ref> These labdanes are [[diterpene]]s (C<sub>20</sub>H<sub>32</sub>) and [[triene]]s, equipping the organic skeleton with three [[alkene]] groups for [[polymerization]]. As amber matures over the years, more polymerization takes place as well as [[isomerization]] reactions, [[Cross-link|crosslinking]] and [[Cyclic compound|cyclization]].<ref>{{Cite book |last=Moldoveanu |first=S.C. |title=Analytical pyrolysis of natural organic polymers |publisher=Elsevier |year=1998}}</ref><ref name=Anderson2023/>

{{Anchor|Oil of amber}}Most amber has a hardness between 2.0 and 2.5 on the [[Mohs scale of mineral hardness|Mohs scale]], a [[refractive index]] of 1.5–1.6, a [[Relative density|specific gravity]] between 1.06 and 1.10, and a melting point of 250–300&nbsp;°C.<ref>{{cite book | last1=Poinar | first1=George O. | last2=Poinar | first2=Hendrik N. | last3=Cano | first3=Raul J. | title=Ancient DNA | chapter=DNA from Amber Inclusions | publisher=Springer New York | location=New York, NY | year=1994 | isbn=978-0-387-94308-4 | doi=10.1007/978-1-4612-4318-2_6 | pages=92–103}}</ref> Heated above {{convert|200|C}}, amber decomposes, yielding an '''oil of amber''', and leaves a black residue which is known as "amber colophony", or "amber pitch"; when dissolved in oil of [[turpentine]] or in [[linseed oil]] this forms "amber varnish" or "amber lac".{{sfn|Rudler|1911|p=792}}

Molecular polymerization,<ref name=Anderson2023/> resulting from high pressures and temperatures produced by overlying sediment, transforms the resin first into [[copal]]. Sustained heat and pressure drives off [[terpene]]s and results in the formation of amber.<ref>{{Cite book | first=Patty C.|last=Rice|title=Amber: Golden Gem of the Ages. 4th Ed.|publisher=AuthorHouse|year=2006|isbn=978-1-4259-3849-9}}</ref> For this to happen, the resin must be resistant to decay. Many trees produce resin, but in the majority of cases this deposit is broken down by physical and biological processes. Exposure to sunlight, rain, microorganisms, and extreme temperatures tends to disintegrate the resin. For the resin to survive long enough to become amber, it must be resistant to such forces or be produced under conditions that exclude them.<ref>Poinar, George O. (1992) ''Life in amber''. Stanford, Calif.: Stanford University Press, p. 12, {{ISBN|0804720010}}</ref> Fossil resins from Europe fall into two categories, the Baltic ambers and another that resembles the ''[[Agathis]]'' group. Fossil resins from the Americas and Africa are closely related to the modern genus ''[[Hymenaea]]'',<ref>{{cite journal |last1=Lambert |first1=JB |last2=Poinar |first2=GO Jr. |year=2002 |title=Amber: the organic gemstone |journal=Accounts of Chemical Research |volume=35 |issue=8 |pages=628–36 |doi=10.1021/ar0001970 |pmid=12186567}}</ref> while Baltic ambers are thought to be fossil resins from plants of the family [[Sciadopityaceae]] that once lived in north Europe.<ref>{{cite journal|last=Wolfe|first=A. P.|author2=Tappert, R.|author3=Muehlenbachs, K.|author4=Boudreau, M.|author5=McKellar, R. C.|author6=Basinger, J. F.|author7=Garrett, A.|title=A new proposal concerning the botanical origin of Baltic amber|journal=Proceedings of the Royal Society B: Biological Sciences|date=30 June 2009|volume=276|issue=1672|pages=3403–3412|doi=10.1098/rspb.2009.0806|pmid=19570786|pmc=2817186}}</ref>[[File:Baltic-amber-fossils-inclusions.jpg|thumb|Baltic amber with inclusions]]
The abnormal development of resin in living trees (''succinosis'') can result in the formation of amber.<ref>{{cite web |last1=Sherborn |first1=Charles Davies |year=1892 |title=Natural Science: A Monthly Review of Scientific Progress, Volume 1 |url=https://books.google.com/books?id=uCzPAAAAMAAJ&q=succinosis&pg=PA379}}</ref> Impurities are quite often present, especially when the resin has dropped onto the ground, so the material may be useless except for varnish-making. Such impure amber is called ''firniss''.<ref>{{Cite book |last=Braswell-Tripp |first=Pearlie |title=Real Diamonds & Precious Stones of the Bible |publisher=Xlibris Corporation |year=2013 |isbn=9781479796441 |location=Bloomington |pages=70 |language=en}}</ref> Such [[Inclusion (mineral)|inclusion]] of other substances can cause the amber to have an unexpected color. [[Pyrite]]s may give a bluish color. ''Bony amber'' owes its cloudy opacity to numerous tiny bubbles inside the resin.{{sfn|Rudler|1911|p=793}} However, so-called ''black amber'' is really a kind of [[Jet (gemstone)|jet]].<ref name="GOPoinar1992">{{cite book | title=Life in Amber | publisher=Stanford University Press | last=Poinar | first=George O.  | year=1992 | location=Stanford, California | page=9}}</ref> In darkly clouded and even opaque amber, inclusions can be imaged using high-energy, high-contrast, high-resolution [[X-ray]]s.<ref>{{cite news |last=Amos |first=Jonathan |date=1 April 2008 |title=BBC News, " Secret 'dino bugs' revealed", 1 April 2008 |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/7324564.stm |url-status=live |archive-url=https://web.archive.org/web/20100828135744/http://news.bbc.co.uk/2/hi/science/nature/7324564.stm |archive-date=28 August 2010}}</ref>[[File:Bernstein Bitterfeld, Gedanit, Bruchstücke 5658.jpg|thumb|Amber from Bitterfeld]]