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<p>[QUOTE=&quot;robinjojo, post: 5057918, member: 110226&quot;]I really like your sestertius - just a&nbsp; wonderful coin.</p><p><br /></p><p>The green deposits are probably malachite.&nbsp; Here is the formula and definition from Sciencedirect.com:</p><p><br /></p><p><i>&quot;Malachite is the another <b>copper carbonate hydroxide</b> mineral with chemical formula [<b>Cu</b>2CO3(<b>OH</b>)2] formed by the weathering of <b>copper</b> orebodies in the vicinity. The color is bright green with light green streak.&quot;</i></p><p><br /></p><p>The surface of the coin undergoes chemical alternation over time.&nbsp; This is true for all metals, with the exception of gold.&nbsp; Copper is very reactive to oxygen, and that is why it darkens rather quickly.&nbsp; Add water, either directly through the soil, or in the form of moisture in the air (or both), and the conditions are present to create carbonate deposits that ultimately, under ideal conditions, create a beautiful patina.</p><p><br /></p><p>Other factors, though can alter the process, creating corrosion and pitting.&nbsp; This is the old Rowan and Martin&#039;s Laugh-in of the 1960s &quot;Fickle Finger of Fate&quot; which applies to coins and just about everything else for that matter.</p><p><br /></p><p>Your coin is a wonderful example as it is.[/QUOTE]</p><p><br /></p>

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