Osmium and Iridium are the two most dense elements in pure form. http://theodoregray.com/PeriodicTable/Elements/077/index.s7.html Which is the most dense element, osmium or iridium? That honor has changed hands a couple of times over the years. How, you might ask? Because measuring the density of a pure element isn't nearly as straightforward as you might think. For one thing, it can be different for different crystalline forms (allotropes) of the same element. For example, diamond is much denser than graphite: Which is the true density of carbon? Both. In the case of metals, it may be impossible to grow single crystals, so you're measuring the density of a polycrystalline mixture, and the density may depend on details of how the material cooled. Minute impurities can also have a big impact on the density.

Supposedly is is Osmium, but there is also talk of it being Iridium. This is from Wikipedia's article on Iridium (http://en.wikipedia.org/wiki/Iridium): "The measured density of this element is only slightly lower than that of osmium, which is often listed as the most dense element known. However, calculations of density from the space lattice may produce more reliable data for these elements than actual measurements and give a density of 22650 kg/m³ for iridium versus 22610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time." Here is a joke I found regarding this question: New Element on Periodic Table A major research institution has just announced the discovery of the densest element yet known to science. The new element has been named "Bushcronium." Bushcronium has one neutron, 12 assistant neutrons, 75 deputy neutrons, and 224 assistant deputy neutrons, giving it an atomic mass of 311. These particles are held together by dark forces called morons, which are surrounded by vast quantities of lepton-like particles called peons. The symbol for Bushcronium is "W". Bushcronium's mass actually increases over time, as morons randomly interact with various elements in the atmosphere and become assistant deputy neutrons in a Bushcronium molecule, forming isodopes. This characteristic of moron-promotion leads some scientists to believe that Bushcronium is formed whenever morons reach a certain quantity in concentration. This hypothetical quantity is referred to as "Critical Morass". When catalyzed with money, Bushcronium activates Foxnewsium, an element that radiates orders of magnitude more energy, albeit as incoherent noise, since it has 1/2 as many peons but twice as many morons.

The human element can be at times.

Pb lead is the most stable dense element all the other elements above that will experience radiactive decay until they become Pb(lead)

Tungsten