When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Up for sale from KeepsCache is an exceptional and massive Limonite after Marcasite Pseudomorph featuring the rare "Jack Straw" crystal habit. This specific specimen was recovered from the Fortress Keep Mine in Jefferson County, Missouri.
What makes this piece a true standout is its incredible preservation. The "Jack Straw" structure—characterized by a chaotic, needle-like lattice of crystals—is notoriously fragile and prone to crushing. Finding a large cabinet-sized specimen weighing 1 lb 11 oz that remains entirely intact is truly a rarity.
The specimen measures approximately 6.5" x 4.5" x 1.75" and displays a sharp, distinct lattice across its entire face. As a pseudomorph, the Limonite has completely replaced the original Marcasite while perfectly maintaining the delicate, haystack-like geometry of the original crystals.
Whether you are a collector of Missouri minerals or a specialist in pseudomorphs and structural habits, this is a museum-quality display piece that represents the best of the Fortress Keep locality.
