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A crystal form can seem to disappear when researchers can no longer reproduce the conditions that created it. In a 2011 report about progesterone, impurities were proposed as one possible reason a particular form had been stable; a separate 2022 study later showed that a missing co-crystal form could be recovered with carefully designed experiments. The cases illustrate a scientific puzzle called polymorphism—not crystals vanishing from a container.
What does it mean for a crystal form to disappear?
A crystal is a solid whose molecules are arranged in an ordered pattern. Polymorphism occurs when the same chemical substance can form more than one such arrangement. The forms share chemical composition but can differ in physical properties, so conditions that produce one arrangement may not produce another.
In this context, “disappearing” means that a previously observed form could not be made again in later experiments. It does not mean that the substance itself ceased to exist, or that the form was proven impossible to recreate.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsThe progesterone puzzle: impurities may have mattered
A 2011 Chemistry World report described researchers’ difficulty reproducing one progesterone polymorph. The researchers compared two forms and found 11 impurities in form 2, compared with three in form 1. They suspected that other steroids introduced during synthesis to induce crystal growth might help explain form 2’s stability relative to form 1.
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That is a proposed explanation, not a complete or confirmed mechanism: the exact structures of the suspected impurities were not identified. Without knowing precisely which impurities were present, recreating the original conditions could be difficult. The report points to a CrystEngComm paper by Lancaster, Harris and Pearson, published in 2011 (volume 13, page 1775; DOI c0ce00858c), but the evidence described does not establish the identity or effect of each impurity.
A later example: researchers recovered a missing co-crystal form
The progesterone report is not proof that an unreproduced form is permanently lost. In a separate case, a 2022 abstract from the International Union of Crystallography described three polymorphs of urea–barbituric acid co-crystals—crystals made from two components. After researchers obtained the P21/c form, they could not reproduce the Cc form under the same or modified conditions, either in their own work or in experiments by other researchers.
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The authors report that electron-density studies and interaction-energy calculations helped them design an experiment that reproduced the missing Cc form and establish conditions for the other two forms. This case shows that understanding the interactions and energetics involved can help guide experiments, though it is a distinct material system from progesterone.
| Case | Material | What the report establishes | What remains uncertain |
|---|---|---|---|
| Progesterone, 2011 | One compound in two crystal forms | The researchers reported 11 impurities in form 2 and three in form 1, and suspected impurities could help explain form 2’s stability. | The exact impurity structures were not identified; the proposed explanation is not a confirmed full mechanism. |
| Urea–barbituric acid, 2022 | A two-component co-crystal with three reported polymorphs | The IUCr abstract says the previously unreproduced Cc form was obtained using experiment design informed by electron-density studies and interaction-energy calculations. | The abstract describes this case; it does not establish that the same approach will recover every missing crystal form. |
Why crystal forms matter in medicines
Different arrangements of the same substance can behave differently, which makes polymorphism important in pharmaceutical development and manufacturing. The 2011 report notes that approval can apply to a particular crystal form; a different, more stable form can therefore create a control challenge.
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The report uses ritonavir as a separate illustration: a second, less soluble form appeared, affected the drug’s performance and required a manufacturing response. This is a contextual example of why crystal form matters, not part of the progesterone study.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is this the same story as the crow and the shiny stones?
No. “The mystery of the disappearing crystals” also appears as the title of a children’s story about a crow taking shiny pebbles and crystals. The science story discussed here is about polymorphs that researchers could not reproduce; the crow tale is unrelated.
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