The image shows a tumbled specimen of unknown origin. This leads to the formation of brecciated jasper, a rock that has - often repeatedly - been shattered, and is made of jasper, and sometimes chalcedony and macrocrystalline quartz of different colors. These movements go on for a long time, the cracks will reopen again, the jasper will be shattered, and the voids in between will be filled with more jasper. The cracks filled out by jasper often form during tectonic activity. Jasper can show many different color patterns, and these have been given their own names, like "landscape jasper", "picture jasper", "poppy jasper", "leopard jasper", "ocean jasper", and so on.
Veins of jasper occasionally occur in igneous rocks (for example, red and yellow jasper in a granite in the Erzgebirge, Saxony, Germany). I haven't seen any geodes filled with jasper that resemble agate geodes, so the formation of jasper seems to be restricted to veins and cracks percolated by aqueous solutions. Jasper is typically found in veins and cracks in volcanic rocks, often together with chalcedony and agate. Some jasper varieties are valued for their peculiar color patterns.
Often it is unevenly colored, either irregularly banded or patchy. Jasper can have a very homogeneous structure and be evenly colored, and is then suitable for lapidary works. Most of the times the streak will be colorless or white, though. The high content of embedded iron compounds occasionally causes the streak to be slightly colored, which is very different from all other quartz varieties. Heliotrope is opaque and thus considered a variety of jasper (see below). It might, for example, be of the same color as a carnelian, but the latter is translucent. Only thin chips of jasper are translucent. What clearly distinguishes jasper from other valuable cryptocrystalline varieties like agate, chrysoprase, sard, or carnelian, is its opacity. Multicolored jasper makes for an interesting ornamental stone, and red jasper is cut as a gemstone.
Jasper of homogeneous color looks a bit like a colored, opaque flint, and shares many of its physical properties, but it forms in different environments. Jasper is not really a mineral in the strict sense, but a mixture of different types of microcrystalline quartz with impurities of other minerals, and is called a textural variety of quartz. Jasper is the name of dense and opaque varieties of microcrystalline quartz.
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